RFC 9559 | Matroska Format | October 2024
Lhomme, et al. | Standards Track | [Page]

Stream:
  Internet Engineering Task Force (IETF)
RFC:
  9559
Updates:
  8794
Category:
  Standards Track
Published:
  October 2024
ISSN:
  2070-1721
Authors:
  S. Lhomme
  M. Bunkus
  D. Rice

# RFC 9559

# Matroska Media Container Format Specification

## Abstract

This document defines the Matroska audiovisual data container structure, including definitions of its structural elements, terminology, vocabulary, and application.¶

This document updates RFC 8794 to permit the use of a previously reserved Extensible Binary Meta Language (EBML) Element ID.¶

## Status of This Memo

This is an Internet Standards Track document.¶

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.¶

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9559.¶

## Copyright Notice

Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved.¶

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶

## 1. Introduction

Matroska is an audiovisual data container format. It was derived from a project called [MCF] but diverges from it significantly because it is based on EBML (Extensible Binary Meta Language) [RFC8794], a binary derivative of XML. EBML provides significant advantages in terms of future format extensibility, without breaking file support in parsers reading the previous versions.¶

To avoid any misunderstandings, it is essential to clarify exactly what an audio/video container is:¶

- It is NOT a video or audio compression format (codec).¶

- It is an envelope in which there can be many audio, video, and subtitles streams, allowing the user to store a complete movie or CD in a single file.¶

Matroska is designed with the future in mind. It incorporates features such as:¶

- Fast seeking in the file¶

- Chapter entries¶

- Full metadata (tags) support¶

- Selectable subtitle/audio/video streams¶

- Modularly expandable¶

- Error resilience (can recover playback even when the stream is damaged)¶

- Streamable over the Internet and local networks (HTTP [RFC9110], FTP [RFC0959], SMB [SMB-CIFS], etc.)¶

- Menus (like menus that DVDs have [DVD-Video])¶

## 2. Status of This Document

This document covers Matroska versions 1, 2, 3, and 4. Matroska version 4 is the current version. Matroska versions 1 to 3 are no longer maintained. No new elements are expected in files with version numbers 1, 2, or 3.¶

## 3. Notation and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

This document defines the following terms in order to define the format and application of Matroska:¶

Matroska:

  A multimedia container format based on EBML (Extensible Binary Meta Language).¶

`Matroska Reader`:

  A data parser that interprets the semantics of a Matroska document and creates a way for programs to use Matroska.¶

`Matroska Player`:

  A `Matroska Reader` with the primary purpose of playing audiovisual files, including Matroska documents.¶

`Matroska Writer`:

  A data writer that creates Matroska documents.¶

## 4. Matroska Overview

### 4.1. Principles

Matroska is a Document Type of EBML. This specification is dependent on the EBML specification [RFC8794]. For an understanding of Matroska's EBML Schema, see in particular the sections of the EBML specification that cover EBML Element Types (Section 7), EBML Schema (Section 11.1), and EBML Structure (Section 3).¶

### 4.2. Updates to RFC 8794

Because of an oversight, [RFC8794] reserved EBML ID 0x80, which is used by deployed Matroska implementations. For this reason, this specification updates [RFC8794] to make 0x80 a legal EBML ID. Additionally, this specification makes the following updates:¶

- Section 17.1 of [RFC8794] (per Erratum ID #7189 [Err7189])¶

OLD:¶

> One-octet Element IDs MUST be between 0x81 and 0xFE. These items are valuable because they are short, and they need to be used for commonly repeated elements. Element IDs are to be allocated within this range according to the "RFC Required" policy [RFC8126].¶

> The following one-octet Element IDs are RESERVED: 0xFF and 0x80.¶

NEW:¶

> One-octet Element IDs MUST be between 0x80 and 0xFE. These items are valuable because they are short, and they need to be used for commonly repeated elements. Element IDs are to be allocated within this range according to the "RFC Required" policy [RFC8126].¶

> The following one-octet Element ID is RESERVED: 0xFF.¶

- Section 5 of [RFC8794] (per Erratum ID #7191 [Err7191])¶

OLD:¶

      +=========================+================+=================+
      | Element ID Octet Length | Range of Valid | Number of Valid |
      |                         |  Element IDs   |     Element IDs |
      +=========================+================+=================+
      |            1            |  0x81 - 0xFE   |             126 |
      +-------------------------+----------------+-----------------+

¶

NEW:¶

      +=========================+================+=================+
      | Element ID Octet Length | Range of Valid | Number of Valid |
      |                         |  Element IDs   |     Element IDs |
      +=========================+================+=================+
      |            1            |  0x80 - 0xFE   |             127 |
      +-------------------------+----------------+-----------------+

¶

### 4.3. Added EBML Constraints

As an EBML Document Type, Matroska adds the following constraints to the EBML specification [RFC8794]:¶

- The `docType` of the `EBML Header` MUST be "matroska".¶

- The `EBMLMaxIDLength` of the `EBML Header` MUST be 4.¶

- The `EBMLMaxSizeLength` of the `EBML Header` MUST be between 1 and 8, inclusive.¶

### 4.4. Design Rules

The `Root Element` and all `Top-Level Elements` MUST use 4 octets for their EBML Element ID -- i.e., `Segment` and direct children of `Segment`.¶

Legacy EBML/Matroska parsers did not handle Empty Elements properly; elements were present in the file but had a length of 0. They always assumed the value was 0 for integers/dates or 0x0p+0, the textual expression of floats using the format in [ISO9899], no matter the default value of the element that should have been used instead. Therefore, `Matroska Writers` MUST NOT use EBML Empty Elements if the element has a default value that is not 0 for integers/dates and 0x0p+0 for floats.¶

When adding new elements to Matroska, these rules apply:¶

- A non-mandatory integer/date Element MUST NOT have a default value other than 0.¶

- A non-mandatory float Element MUST NOT have a default value other than 0x0p+0.¶

- A non-mandatory string Element MUST NOT have a default value, as empty strings cannot be defined in the XML Schema.¶

### 4.5. Data Layout

A Matroska file MUST be composed of at least one `EBML Document` using the `Matroska Document Type`. Each `EBML Document` MUST start with an `EBML Header` and MUST be followed by the `EBML Root Element`, defined as `Segment` in Matroska. Matroska defines several `Top-Level Elements` that may occur within the `Segment`.¶

As an example, a simple Matroska file consisting of a single `EBML Document` could be represented like this:¶

- `EBML Header`¶
- `Segment`¶

A more complex Matroska file consisting of an `EBML Stream` (consisting of two `EBML Documents`) could be represented like this:¶

- `EBML Header`¶
- `Segment`¶
- `EBML Header`¶
- `Segment`¶

The following diagram represents a simple Matroska file, comprised of an `EBML Document` with an `EBML Header`, a `Segment` element (the `Root Element`), and all eight Matroska `Top-Level Elements`. In the diagrams in this section, horizontal spacing expresses a parent-child relationship between Matroska elements (e.g., the `Info` element is contained within the `Segment` element), whereas vertical alignment represents the storage order within the file.¶

    +-------------+
    | EBML Header |
    +---------------------------+
    | Segment     | SeekHead    |
    |             |-------------|
    |             | Info        |
    |             |-------------|
    |             | Tracks      |
    |             |-------------|
    |             | Chapters    |
    |             |-------------|
    |             | Cluster     |
    |             |-------------|
    |             | Cues        |
    |             |-------------|
    |             | Attachments |
    |             |-------------|
    |             | Tags        |
    +---------------------------+

Figure 1: Basic Layout of a Matroska File

The Matroska `EBML Schema` defines eight `Top-Level Elements`:¶

- `SeekHead` (Section 6.3)¶

- `Info` (Section 6.5)¶

- `Tracks` (Section 18)¶

- `Chapters` (Section 20)¶

- `Cluster` (Section 10)¶

- `Cues` (Section 22)¶

- `Attachments` (Section 21)¶

- `Tags` (Section 6.8)¶

The `SeekHead` element (also known as `MetaSeek`) contains an index of `Top-Level Elements` locations within the `Segment`. Use of the `SeekHead` element is RECOMMENDED. Without a `SeekHead` element, a Matroska parser would have to search the entire file to find all of the other `Top-Level Elements`. This is due to Matroska's flexible ordering requirements; for instance, it is acceptable for the `Chapters` element to be stored after the `Cluster` element(s).¶

    +--------------------------------+
    | SeekHead | Seek | SeekID       |
    |          |      |--------------|
    |          |      | SeekPosition |
    +--------------------------------+

Figure 2: Representation of a `SeekHead` Element

The `Info` element contains vital information for identifying the whole `Segment`. This includes the title for the `Segment`, a randomly generated unique identifier (UID), and the UID(s) of any linked `Segment` elements.¶

    +-------------------------+
    | Info | SegmentUUID      |
    |      |------------------|
    |      | SegmentFilename  |
    |      |------------------|
    |      | PrevUUID         |
    |      |------------------|
    |      | PrevFilename     |
    |      |------------------|
    |      | NextUUID         |
    |      |------------------|
    |      | NextFilename     |
    |      |------------------|
    |      | SegmentFamily    |
    |      |------------------|
    |      | ChapterTranslate |
    |      |------------------|
    |      | TimestampScale   |
    |      |------------------|
    |      | Duration         |
    |      |------------------|
    |      | DateUTC          |
    |      |------------------|
    |      | Title            |
    |      |------------------|
    |      | MuxingApp        |
    |      |------------------|
    |      | WritingApp       |
    |-------------------------|

Figure 3: Representation of an `Info` Element and Its `Child Elements`

The `Tracks` element defines the technical details for each track and can store the name, number, UID, language, and type (audio, video, subtitles, etc.) of each track. For example, the `Tracks` element MAY store information about the resolution of a video track or sample rate of an audio track.¶

The `Tracks` element MUST identify all the data needed by the codec to decode the data of the specified track. However, the data required is contingent on the codec used for the track. For example, a `Track` element for uncompressed audio only requires the audio bit rate to be present. A codec such as AC-3 would require that the `CodecID` element be present for all tracks, as it is the primary way to identify which codec to use to decode the track.¶

    +------------------------------------+
    | Tracks | TrackEntry | TrackNumber  |
    |        |            |--------------|
    |        |            | TrackUID     |
    |        |            |--------------|
    |        |            | TrackType    |
    |        |            |--------------|
    |        |            | Name         |
    |        |            |--------------|
    |        |            | Language     |
    |        |            |--------------|
    |        |            | CodecID      |
    |        |            |--------------|
    |        |            | CodecPrivate |
    |        |            |--------------|
    |        |            | CodecName    |
    |        |            |----------------------------------+
    |        |            | Video        | FlagInterlaced    |
    |        |            |              |-------------------|
    |        |            |              | FieldOrder        |
    |        |            |              |-------------------|
    |        |            |              | StereoMode        |
    |        |            |              |-------------------|
    |        |            |              | AlphaMode         |
    |        |            |              |-------------------|
    |        |            |              | PixelWidth        |
    |        |            |              |-------------------|
    |        |            |              | PixelHeight       |
    |        |            |              |-------------------|
    |        |            |              | DisplayWidth      |
    |        |            |              |-------------------|
    |        |            |              | DisplayHeight     |
    |        |            |              |-------------------|
    |        |            |              | AspectRatioType   |
    |        |            |              |-------------------|
    |        |            |              | Colour            |
    |        |            |----------------------------------|
    |        |            | Audio        | SamplingFrequency |
    |        |            |              |-------------------|
    |        |            |              | Channels          |
    |        |            |              |-------------------|
    |        |            |              | BitDepth          |
    |--------------------------------------------------------|

Figure 4: Representation of the `Tracks` Element and a Selection of Its `Descendant` Elements

The `Chapters` element lists all of the chapters. `Chapters` are a way to set predefined points to jump to in video or audio.¶

    +-----------------------------------------+
    | Chapters | Edition | EditionUID         |
    |          | Entry   |--------------------|
    |          |         | EditionFlagDefault |
    |          |         |--------------------|
    |          |         | EditionFlagOrdered |
    |          |         |---------------------------------+
    |          |         | ChapterAtom | ChapterUID        |
    |          |         |             |-------------------|
    |          |         |             | ChapterStringUID  |
    |          |         |             |-------------------|
    |          |         |             | ChapterTimeStart  |
    |          |         |             |-------------------|
    |          |         |             | ChapterTimeEnd    |
    |          |         |             |-------------------|
    |          |         |             | ChapterFlagHidden |
    |          |         |             |-------------------------------+
    |          |         |             | ChapterDisplay | ChapString   |
    |          |         |             |                |--------------|
    |          |         |             |                | ChapLanguage |
    +------------------------------------------------------------------+

Figure 5: Representation of the `Chapters` Element and a Selection of Its `Descendant` Elements

`Cluster` elements contain the content for each track, e.g., video frames. A Matroska file SHOULD contain at least one `Cluster` element. In the rare case it doesn't, there should be a method for `Segments` to link together, possibly using `Chapters`; see Section 17.¶

The `Cluster` element helps to break up `SimpleBlock` or `BlockGroup` elements and helps with seeking and error protection. Every `Cluster` element MUST contain a `Timestamp` element. This SHOULD be the `Timestamp` element used to play the first `Block` in the `Cluster` element, unless a different value is needed to accommodate for more `Blocks`; see Section 11.2.¶

`Cluster` elements contain one or more `Block` element, such as `BlockGroup` or `SimpleBlock` elements. In some situations, a `Cluster` element MAY contain no `Block` element, for example, in a live recording when no data has been collected.¶

A `BlockGroup` element MAY contain a `Block` of data and any information relating directly to that `Block`.¶

    +--------------------------+
    | Cluster | Timestamp      |
    |         |----------------|
    |         | Position       |
    |         |----------------|
    |         | PrevSize       |
    |         |----------------|
    |         | SimpleBlock    |
    |         |----------------|
    |         | BlockGroup     |
    +--------------------------+

Figure 6: Representation of a `Cluster` Element and Its Immediate `Child Elements`

    +----------------------------------+
    | Block | Portion of | Data Type   |
    |       | a Block    |  - Bit Flag |
    |       |--------------------------+
    |       | Header     | TrackNumber |
    |       |            |-------------|
    |       |            | Timestamp   |
    |       |            |-------------|
    |       |            | Flags       |
    |       |            |  - Gap      |
    |       |            |  - Lacing   |
    |       |            |  - Reserved |
    |       |--------------------------|
    |       | Optional   | FrameSize   |
    |       |--------------------------|
    |       | Data       | Frame       |
    +----------------------------------+

Figure 7: Representation of the `Block` Element Structure

Each `Cluster` MUST contain exactly one `Timestamp` element. The `Timestamp` element value MUST be stored once per `Cluster`. The `Timestamp` element in the `Cluster` is relative to the entire `Segment`. The `Timestamp` element SHOULD be the first element in the `Cluster` it belongs to or the second element if that `Cluster` contains a `CRC-32` element (Section 6.2).¶

Additionally, the `Block` contains an offset that, when added to the `Cluster`'s `Timestamp` element value, yields the `Block`'s effective timestamp. Therefore, the timestamp in the `Block` itself is relative to the `Timestamp` element in the `Cluster`. For example, if the `Timestamp` element in the `Cluster` is set to 10 seconds and a `Block` in that `Cluster` is supposed to be played 12 seconds into the clip, the timestamp in the `Block` would be set to 2 seconds.¶

The `ReferenceBlock` in the `BlockGroup` is used instead of the basic "P-frame"/"B-frame" description. Instead of simply saying that this `Block` depends on the `Block` directly before or directly after, the `Timestamp` of the necessary `Block` is used. Because there can be as many `ReferenceBlock` elements as necessary for a `Block`, it allows for some extremely complex referencing.¶

The `Cues` element is used to seek when playing back a file by providing a temporal index for some of the `Tracks`. It is similar to the `SeekHead` element but is used for seeking to a specific time when playing back the file. It is possible to seek without this element, but it is much more difficult because a `Matroska Reader` would have to "hunt and peck" through the file to look for the correct timestamp.¶

The `Cues` element SHOULD contain at least one `CuePoint` element. Each `CuePoint` element stores the position of the `Cluster` that contains the `BlockGroup` or `SimpleBlock` element. The timestamp is stored in the `CueTime` element, and the location is stored in the `CueTrackPositions` element.¶

The `Cues` element is flexible. For instance, the `Cues` element can be used to index every single timestamp of every `Block` or they can be indexed selectively.¶

    +-------------------------------------+
    | Cues | CuePoint | CueTime           |
    |      |          |-------------------|
    |      |          | CueTrackPositions |
    |      |------------------------------|
    |      | CuePoint | CueTime           |
    |      |          |-------------------|
    |      |          | CueTrackPositions |
    +-------------------------------------+

Figure 8: Representation of a `Cues` Element and Two Levels of Its `Descendant` Elements

The `Attachments` element is for attaching files to a Matroska file, such as pictures, fonts, web pages, etc.¶

    +------------------------------------------------+
    | Attachments | AttachedFile | FileDescription   |
    |             |              |-------------------|
    |             |              | FileName          |
    |             |              |-------------------|
    |             |              | FileMediaType     |
    |             |              |-------------------|
    |             |              | FileData          |
    |             |              |-------------------|
    |             |              | FileUID           |
    +------------------------------------------------+

Figure 9: Representation of an `Attachments` Element

The `Tags` element contains metadata that describes the `Segment` and potentially its `Tracks`, `Chapters`, and `Attachments`. Each `Track` or `Chapter` that those tags applies to has its UID listed in the `Tags`. The `Tags` contain all extra information about the file: scriptwriters, singers, actors, directors, titles, edition, price, dates, genre, comments, etc. `Tags` can contain their values in multiple languages. For example, a movie's "TITLE" tag value might contain both the original English title as well as the German title.¶

    +-------------------------------------------+
    | Tags | Tag | Targets   | TargetTypeValue  |
    |      |     |           |------------------|
    |      |     |           | TargetType       |
    |      |     |           |------------------|
    |      |     |           | TagTrackUID      |
    |      |     |           |------------------|
    |      |     |           | TagEditionUID    |
    |      |     |           |------------------|
    |      |     |           | TagChapterUID    |
    |      |     |           |------------------|
    |      |     |           | TagAttachmentUID |
    |      |     |------------------------------|
    |      |     | SimpleTag | TagName          |
    |      |     |           |------------------|
    |      |     |           | TagLanguage      |
    |      |     |           |------------------|
    |      |     |           | TagDefault       |
    |      |     |           |------------------|
    |      |     |           | TagString        |
    |      |     |           |------------------|
    |      |     |           | TagBinary        |
    |      |     |           |------------------|
    |      |     |           | SimpleTag        |
    +-------------------------------------------+

Figure 10: Representation of a `Tags` Element and Three Levels of Its `Children Elements`

## 5. Matroska Schema

This specification includes an `EBML Schema` that defines the elements and structure of Matroska using the EBML Schema elements and attributes defined in Section 11.1 of [RFC8794].¶

Attributes using their default value (like `minOccurs`, `minver`, etc.) or attributes with undefined values (like `length`, `maxver`, etc.) are omitted.¶

The definitions for each Matroska element are provided below.¶

### 5.1. Segment Element

id / type:
  0x18538067 / master¶
unknownsizeallowed:
  True¶
path:
  `\Segment`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The `Root Element` that contains all other `Top-Level Elements`; see Section 4.5.¶

#### 5.1.1. SeekHead Element

id / type:
  0x114D9B74 / master¶
path:
  `\Segment\SeekHead`¶
maxOccurs:
  2¶
definition:
  Contains seeking information of `Top-Level Elements`; see Section 4.5.¶

##### 5.1.1.1. Seek Element

id / type:
  0x4DBB / master¶
path:
  `\Segment\SeekHead\Seek`¶
minOccurs:
  1¶
definition:
  Contains a single seek entry to an EBML Element.¶

###### 5.1.1.1.1. SeekID Element

id / type:
  0x53AB / binary¶
length:
  4¶
path:
  `\Segment\SeekHead\Seek\SeekID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The binary EBML ID of a `Top-Level Element`.¶

###### 5.1.1.1.2. SeekPosition Element

id / type:
  0x53AC / uinteger¶
path:
  `\Segment\SeekHead\Seek\SeekPosition`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The `Segment Position` (Section 16) of a `Top-Level Element`.¶

#### 5.1.2. Info Element

id / type:
  0x1549A966 / master¶
path:
  `\Segment\Info`¶
minOccurs / maxOccurs:
  1 / 1¶
recurring:
  True¶
definition:
  Contains general information about the `Segment`.¶

##### 5.1.2.1. SegmentUUID Element

id / type:
  0x73A4 / binary¶
length:
  16¶
path:
  `\Segment\Info\SegmentUUID`¶
maxOccurs:
  1¶
definition:
  A randomly generated UID that identifies the `Segment` amongst many others (128 bits). It is equivalent to a Universally Unique Identifier (UUID) v4 [RFC9562] with all bits randomly (or pseudorandomly) chosen. An actual UUID v4 value, where some bits are not random, MAY also be used.¶
usage notes:
  If the `Segment` is a part of a `Linked Segment`, then this element is REQUIRED. The value of the UID MUST contain at least one bit set to 1.¶

##### 5.1.2.2. SegmentFilename Element

id / type:
  0x7384 / utf-8¶
path:
  `\Segment\Info\SegmentFilename`¶
maxOccurs:
  1¶
definition:
  A filename corresponding to this `Segment`.¶

##### 5.1.2.3. PrevUUID Element

id / type:
  0x3CB923 / binary¶
length:
  16¶
path:
  `\Segment\Info\PrevUUID`¶
maxOccurs:
  1¶
definition:
  An ID that identifies the previous `Segment` of a `Linked Segment`.¶
usage notes:
  If the `Segment` is a part of a `Linked Segment` that uses Hard Linking (Section 17.1), then either the `PrevUUID` or the `NextUUID` element is REQUIRED. If a `Segment` contains a `PrevUUID` but not a `NextUUID`, then it MAY be considered as the last `Segment` of the `Linked Segment`. The `PrevUUID` MUST NOT be equal to the `SegmentUUID`.¶

##### 5.1.2.4. PrevFilename Element

id / type:
  0x3C83AB / utf-8¶
path:
  `\Segment\Info\PrevFilename`¶
maxOccurs:
  1¶
definition:
  A filename corresponding to the file of the previous `Linked Segment`.¶
usage notes:
  Provision of the previous filename is for display convenience, but `PrevUUID` SHOULD be considered authoritative for identifying the previous `Segment` in a `Linked Segment`.¶

##### 5.1.2.5. NextUUID Element

id / type:
  0x3EB923 / binary¶
length:
  16¶
path:
  `\Segment\Info\NextUUID`¶
maxOccurs:
  1¶
definition:
  An ID that identifies the next `Segment` of a `Linked Segment`.¶
usage notes:
  If the `Segment` is a part of a `Linked Segment` that uses Hard Linking (Section 17.1), then either the `PrevUUID` or the `NextUUID` element is REQUIRED. If a `Segment` contains a `NextUUID` but not a `PrevUUID`, then it MAY be considered as the first `Segment` of the `Linked Segment`. The `NextUUID` MUST NOT be equal to the `SegmentUUID`.¶

##### 5.1.2.6. NextFilename Element

id / type:
  0x3E83BB / utf-8¶
path:
  `\Segment\Info\NextFilename`¶
maxOccurs:
  1¶
definition:
  A filename corresponding to the file of the next `Linked Segment`.¶
usage notes:
  Provision of the next filename is for display convenience, but `NextUUID` SHOULD be considered authoritative for identifying the Next `Segment`.¶

##### 5.1.2.7. SegmentFamily Element

id / type:
  0x4444 / binary¶
length:
  16¶
path:
  `\Segment\Info\SegmentFamily`¶
definition:
  A UID that all `Segments` of a `Linked Segment` MUST share (128 bits). It is equivalent to a UUID v4 [RFC9562] with all bits randomly (or pseudorandomly) chosen. An actual UUID v4 value, where some bits are not random, MAY also be used.¶
usage notes:
  If the `Segment` `Info` contains a `ChapterTranslate` element, this element is REQUIRED.¶

##### 5.1.2.8. ChapterTranslate Element

id / type:
  0x6924 / master¶
path:
  `\Segment\Info\ChapterTranslate`¶
definition:
  The mapping between this `Segment` and a segment value in the given Chapter Codec.¶
rationale:
  Chapter Codecs may need to address different segments, but they may not know of the way to identify such segments when stored in Matroska. This element and its child elements add a way to map the internal segments known to the Chapter Codec to the `SegmentUUID`s in Matroska. This allows remuxing a file with Chapter Codec without changing the content of the codec data, just the `Segment` mapping.¶

###### 5.1.2.8.1. ChapterTranslateID Element

id / type:
  0x69A5 / binary¶
path:
  `\Segment\Info\ChapterTranslate\ChapterTranslateID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The binary value used to represent this `Segment` in the chapter codec data. The format depends on the `ChapProcessCodecID` used; see Section 5.1.7.1.4.15.¶

###### 5.1.2.8.2. ChapterTranslateCodec Element

id / type:
  0x69BF / uinteger¶
path:
  `\Segment\Info\ChapterTranslate\ChapterTranslateCodec`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Applies to the chapter codec of the given chapter edition(s); see Section 5.1.7.1.4.15.¶
defined values:
  See Table 31. Additional values can be registered in the "Matroska Chapter Codec IDs" registry defined in Section 27.14.¶

###### 5.1.2.8.3. ChapterTranslateEditionUID Element

id / type:
  0x69FC / uinteger¶
path:
  `\Segment\Info\ChapterTranslate\ChapterTranslateEditionUID`¶
definition:
  Specifies a chapter edition UID to which this `ChapterTranslate` applies.¶
usage notes:
  When no `ChapterTranslateEditionUID` is specified in the `ChapterTranslate`, the `ChapterTranslate` applies to all chapter editions found in the `Segment` using the given `ChapterTranslateCodec`.¶

##### 5.1.2.9. TimestampScale Element

id / type / default:
  0x2AD7B1 / uinteger / 1000000¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Info\TimestampScale`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Base unit for Segment Ticks and Track Ticks, in nanoseconds. A `TimestampScale` value of 1000000 means scaled timestamps in the `Segment` are expressed in milliseconds; see Section 11 on how to interpret timestamps.¶

##### 5.1.2.10. Duration Element

id / type:
  0x4489 / float¶
range:
  > 0x0p+0¶
path:
  `\Segment\Info\Duration`¶
maxOccurs:
  1¶
definition:
  Duration of the `Segment`, expressed in `Segment` Ticks, which are based on `TimestampScale`; see Section 11.1.¶

##### 5.1.2.11. DateUTC Element

id / type:
  0x4461 / date¶
path:
  `\Segment\Info\DateUTC`¶
maxOccurs:
  1¶
definition:
  The date and time that the `Segment` was created by the muxing application or library.¶

##### 5.1.2.12. Title Element

id / type:
  0x7BA9 / utf-8¶
path:
  `\Segment\Info\Title`¶
maxOccurs:
  1¶
definition:
  General name of the `Segment`.¶

##### 5.1.2.13. MuxingApp Element

id / type:
  0x4D80 / utf-8¶
path:
  `\Segment\Info\MuxingApp`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Muxing application or library (example: "libmatroska-0.4.3").¶
usage notes:
  Include the full name of the application or library followed by the version number.¶

##### 5.1.2.14. WritingApp Element

id / type:
  0x5741 / utf-8¶
path:
  `\Segment\Info\WritingApp`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Writing application (example: "mkvmerge-0.3.3").¶
usage notes:
  Include the full name of the application followed by the version number.¶

#### 5.1.3. Cluster Element

id / type:
  0x1F43B675 / master¶
unknownsizeallowed:
  True¶
path:
  `\Segment\Cluster`¶
definition:
  The `Top-Level Element` containing the (monolithic) `Block` structure.¶

##### 5.1.3.1. Timestamp Element

id / type:
  0xE7 / uinteger¶
path:
  `\Segment\Cluster\Timestamp`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Absolute timestamp of the cluster, expressed in Segment Ticks, which are based on `TimestampScale`; see Section 11.1.¶
usage notes:
  This element SHOULD be the first child element of the `Cluster` it belongs to or the second if that `Cluster` contains a `CRC-32` element (Section 6.2).¶

##### 5.1.3.2. Position Element

id / type:
  0xA7 / uinteger¶
path:
  `\Segment\Cluster\Position`¶
maxOccurs:
  1¶
maxver:
  4¶
definition:
  The `Segment Position` of the `Cluster` in the `Segment` (0 in live streams). It might help to resynchronize the offset on damaged streams.¶

##### 5.1.3.3. PrevSize Element

id / type:
  0xAB / uinteger¶
path:
  `\Segment\Cluster\PrevSize`¶
maxOccurs:
  1¶
definition:
  Size of the previous `Cluster`, in octets. Can be useful for backward playing.¶

##### 5.1.3.4. SimpleBlock Element

id / type:
  0xA3 / binary¶
path:
  `\Segment\Cluster\SimpleBlock`¶
minver:
  2¶
definition:
  Similar to `Block` (see Section 10.1) but without all the extra information. Mostly used to reduce overhead when no extra feature is needed; see Section 10.2 on `SimpleBlock` Structure.¶

##### 5.1.3.5. BlockGroup Element

id / type:
  0xA0 / master¶
path:
  `\Segment\Cluster\BlockGroup`¶
definition:
  Basic container of information containing a single `Block` and information specific to that `Block`.¶

###### 5.1.3.5.1. Block Element

id / type:
  0xA1 / binary¶
path:
  `\Segment\Cluster\BlockGroup\Block`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  `Block` containing the actual data to be rendered and a timestamp relative to the `Cluster` Timestamp; see Section 10.1 on `Block` Structure.¶

###### 5.1.3.5.2. BlockAdditions Element

id / type:
  0x75A1 / master¶
path:
  `\Segment\Cluster\BlockGroup\BlockAdditions`¶
maxOccurs:
  1¶
definition:
  Contains additional binary data to complete the `Block` element; see Section 4.1.5 of [MatroskaCodec] for more information. An EBML parser that has no knowledge of the `Block` structure could still see and use/skip these data.¶

###### 5.1.3.5.2.1. BlockMore Element

id / type:
  0xA6 / master¶
path:
  `\Segment\Cluster\BlockGroup\BlockAdditions\BlockMore`¶
minOccurs:
  1¶
definition:
  Contains the `BlockAdditional` and some parameters.¶

###### 5.1.3.5.2.2. BlockAdditional Element

id / type:
  0xA5 / binary¶
path:
  `\Segment\Cluster\BlockGroup\BlockAdditions\BlockMore\BlockAdditional`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Interpreted by the codec as it wishes (using the `BlockAddID`).¶

###### 5.1.3.5.2.3. BlockAddID Element

id / type / default:
  0xEE / uinteger / 1¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Cluster\BlockGroup\BlockAdditions\BlockMore\BlockAddID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  An ID that identifies how to interpret the `BlockAdditional` data; see Section 4.1.5 of [MatroskaCodec] for more information. A value of 1 indicates that the `BlockAdditional` data is defined by the codec. Any other value indicates that the `BlockAdditional` data should be handled according to the `BlockAddIDType` that is located in the `TrackEntry`.¶
usage notes:
  Each `BlockAddID` value MUST be unique between all `BlockMore` elements found in a `BlockAdditions` element. To keep `MaxBlockAdditionID` as low as possible, small values SHOULD be used.¶

###### 5.1.3.5.3. BlockDuration Element

id / type:
  0x9B / uinteger¶
path:
  `\Segment\Cluster\BlockGroup\BlockDuration`¶
minOccurs / maxOccurs:
  See Table 1 / 1¶
definition:
  The duration of the `Block`, expressed in Track Ticks; see Section 11.1. The `BlockDuration` element can be useful at the end of a `Track` to define the duration of the last frame (as there is no subsequent `Block` available) or when there is a break in a track like for subtitle tracks.¶
notes:
  See Table 1.¶

Table 1: BlockDuration Implementation Notes
attribute | note
--- | ---
minOccurs | `BlockDuration` MUST be set (minOccurs=1) if the associated `TrackEntry` stores a `DefaultDuration` value.
default | If a value is not present and no `DefaultDuration` is defined, the value is assumed to be the difference between the timestamp of this `Block` and the timestamp of the next `Block` in "display" order (not coding order).

###### 5.1.3.5.4. ReferencePriority Element

id / type / default:
  0xFA / uinteger / 0¶
path:
  `\Segment\Cluster\BlockGroup\ReferencePriority`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  This frame is referenced and has the specified cache priority. In the cache, only a frame of the same or higher priority can replace this frame. A value of 0 means the frame is not referenced.¶

###### 5.1.3.5.5. ReferenceBlock Element

id / type:
  0xFB / integer¶
path:
  `\Segment\Cluster\BlockGroup\ReferenceBlock`¶
definition:
  A timestamp value, relative to the timestamp of the `Block` in this `BlockGroup`, expressed in Track Ticks; see Section 11.1. This is used to reference other frames necessary to decode this frame. The relative value SHOULD correspond to a valid `Block` that this `Block` depends on. Historically, `Matroska Writers` didn't write the actual `Block(s)` that this `Block` depends on, but they did write some `Block(s)` in the past.¶

The value "0" MAY also be used to signify that this `Block` cannot be decoded on its own, but the necessary reference `Block(s)` is unknown. In this case, other `ReferenceBlock` elements MUST NOT be found in the same `BlockGroup`. If the `BlockGroup` doesn't have a `ReferenceBlock` element, then the `Block` it contains can be decoded without using any other `Block` data.¶

###### 5.1.3.5.6. CodecState Element

id / type:
  0xA4 / binary¶
path:
  `\Segment\Cluster\BlockGroup\CodecState`¶
maxOccurs:
  1¶
minver:
  2¶
definition:
  The new codec state to use. Data interpretation is private to the codec. This information SHOULD always be referenced by a seek entry.¶

###### 5.1.3.5.7. DiscardPadding Element

id / type:
  0x75A2 / integer¶
path:
  `\Segment\Cluster\BlockGroup\DiscardPadding`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Duration of the silent data added to the `Block`, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1 (padding at the end of the `Block` for positive values and at the beginning of the `Block` for negative values). The duration of `DiscardPadding` is not calculated in the duration of the `TrackEntry` and SHOULD be discarded during playback.¶

#### 5.1.4. Tracks Element

id / type:
  0x1654AE6B / master¶
path:
  `\Segment\Tracks`¶
maxOccurs:
  1¶
recurring:
  True¶
definition:
  A `Top-Level Element` of information with many tracks described.¶

##### 5.1.4.1. TrackEntry Element

id / type:
  0xAE / master¶
path:
  `\Segment\Tracks\TrackEntry`¶
minOccurs:
  1¶
definition:
  Describes a track with all elements.¶

###### 5.1.4.1.1. TrackNumber Element

id / type:
  0xD7 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\TrackNumber`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The track number as used in the `Block` Header.¶

###### 5.1.4.1.2. TrackUID Element

id / type:
  0x73C5 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\TrackUID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  A UID that identifies the `Track`.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.3. TrackType Element

id / type:
  0x83 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\TrackType`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The `TrackType` defines the type of each frame found in the `Track`. The value SHOULD be stored on 1 octet.¶
defined values:
  See Table 2. Additional values can be registered in the "Matroska Track Types" registry defined in Section 27.16.¶
stream copy:
  True (Section 8)¶

Table 2: TrackType Values
value | label | contents of each frame
--- | --- | ---
`1` | video | An image.
`2` | audio | Audio samples.
`3` | complex | A mix of different other `TrackType`. The codec needs to define how the `Matroska Player` should interpret such data.
`16` | logo | An image to be rendered over the video track(s).
`17` | subtitle | Subtitle or closed caption data to be rendered over the video track(s).
`18` | buttons | Interactive button(s) to be rendered over the video track(s).
`32` | control | Metadata used to control the player of the `Matroska Player`.
`33` | metadata | Timed metadata that can be passed on to the `Matroska Player`.

###### 5.1.4.1.4. FlagEnabled Element

id / type / default:
  0xB9 / uinteger / 1¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagEnabled`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  2¶
definition:
  Set to 1 if the track is usable. It is possible to turn a track that is not usable into a usable track using chapter codecs or control tracks.¶

###### 5.1.4.1.5. FlagDefault Element

id / type / default:
  0x88 / uinteger / 1¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagDefault`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Set to 1 if the track (audio, video, or subtitles) is eligible for automatic selection by the player; see Section 19 for more details.¶

###### 5.1.4.1.6. FlagForced Element

id / type / default:
  0x55AA / uinteger / 0¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagForced`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Applies only to subtitles. Set to 1 if the track is eligible for automatic selection by the player if it matches the user's language preference, even if the user's preferences would not normally enable subtitles with the selected audio track; this can be used for tracks containing only translations of audio in foreign languages or on-screen text. See Section 19 for more details.¶

###### 5.1.4.1.7. FlagHearingImpaired Element

id / type:
  0x55AB / uinteger¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagHearingImpaired`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Set to 1 if and only if the track is suitable for users with hearing impairments.¶

###### 5.1.4.1.8. FlagVisualImpaired Element

id / type:
  0x55AC / uinteger¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagVisualImpaired`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Set to 1 if and only if the track is suitable for users with visual impairments.¶

###### 5.1.4.1.9. FlagTextDescriptions Element

id / type:
  0x55AD / uinteger¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagTextDescriptions`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Set to 1 if and only if the track contains textual descriptions of video content.¶

###### 5.1.4.1.10. FlagOriginal Element

id / type:
  0x55AE / uinteger¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagOriginal`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Set to 1 if and only if the track is in the content's original language.¶

###### 5.1.4.1.11. FlagCommentary Element

id / type:
  0x55AF / uinteger¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagCommentary`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Set to 1 if and only if the track contains commentary.¶

###### 5.1.4.1.12. FlagLacing Element

id / type / default:
  0x9C / uinteger / 1¶
range:
  0-1¶
path:
  `\Segment\Tracks\TrackEntry\FlagLacing`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Set to 1 if the track MAY contain blocks that use lacing. When set to 0, all blocks MUST have their lacing flags set to "no lacing"; see Section 10.3 on 'Block' Lacing.¶

###### 5.1.4.1.13. DefaultDuration Element

id / type:
  0x23E383 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\DefaultDuration`¶
maxOccurs:
  1¶
definition:
  Number of nanoseconds per frame, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1 ("frame" in the Matroska sense -- one element put into a (Simple)Block).¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.14. DefaultDecodedFieldDuration Element

id / type:
  0x234E7A / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\DefaultDecodedFieldDuration`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The period between two successive fields at the output of the decoding process, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1. See Section 9 for more information.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.15. TrackTimestampScale Element

id / type / default:
  0x23314F / float / 0x1p+0¶
range:
  > 0x0p+0¶
path:
  `\Segment\Tracks\TrackEntry\TrackTimestampScale`¶
minOccurs / maxOccurs:
  1 / 1¶
maxver:
  3¶
definition:
  The scale to apply on this track to work at normal speed in relation with other tracks (mostly used to adjust video speed when the audio length differs).¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.16. MaxBlockAdditionID Element

id / type / default:
  0x55EE / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\MaxBlockAdditionID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The maximum value of `BlockAddID` (Section 5.1.3.5.2.3). A value of 0 means there is no `BlockAdditions` (Section 5.1.3.5.2) for this track.¶

###### 5.1.4.1.17. BlockAdditionMapping Element

id / type:
  0x41E4 / master¶
path:
  `\Segment\Tracks\TrackEntry\BlockAdditionMapping`¶
minver:
  4¶
definition:
  Contains elements that extend the track format by adding content either to each frame, with `BlockAddID` (Section 5.1.3.5.2.3), or to the track as a whole with `BlockAddIDExtraData`.¶

###### 5.1.4.1.17.1. BlockAddIDValue Element

id / type:
  0x41F0 / uinteger¶
range:
  >=2¶
path:
  `\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDValue`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  If the track format extension needs content beside frames, the value refers to the `BlockAddID` (Section 5.1.3.5.2.3) value being described.¶
usage notes:
  To keep `MaxBlockAdditionID` as low as possible, small values SHOULD be used.¶

###### 5.1.4.1.17.2. BlockAddIDName Element

id / type:
  0x41A4 / string¶
path:
  `\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDName`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  A human-friendly name describing the type of `BlockAdditional` data, as defined by the associated `Block Additional Mapping`.¶

###### 5.1.4.1.17.3. BlockAddIDType Element

id / type / default:
  0x41E7 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDType`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Stores the registered identifier of the `Block Additional Mapping` to define how the `BlockAdditional` data should be handled.¶
usage notes:
  If `BlockAddIDType` is 0, the `BlockAddIDValue` and corresponding `BlockAddID` values MUST be 1.¶

###### 5.1.4.1.17.4. BlockAddIDExtraData Element

id / type:
  0x41ED / binary¶
path:
  `\Segment\Tracks\TrackEntry\BlockAdditionMapping\BlockAddIDExtraData`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Extra binary data that the `BlockAddIDType` can use to interpret the `BlockAdditional` data. The interpretation of the binary data depends on the `BlockAddIDType` value and the corresponding `Block Additional Mapping`.¶

###### 5.1.4.1.18. Name Element

id / type:
  0x536E / utf-8¶
path:
  `\Segment\Tracks\TrackEntry\Name`¶
maxOccurs:
  1¶
definition:
  A human-readable track name.¶

###### 5.1.4.1.19. Language Element

id / type / default:
  0x22B59C / string / eng¶
path:
  `\Segment\Tracks\TrackEntry\Language`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The language of the track, in the Matroska languages form; see Section 12 on language codes. This element MUST be ignored if the `LanguageBCP47` element is used in the same `TrackEntry`.¶

###### 5.1.4.1.20. LanguageBCP47 Element

id / type:
  0x22B59D / string¶
path:
  `\Segment\Tracks\TrackEntry\LanguageBCP47`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The language of the track, in the form defined in [RFC5646]; see Section 12 on language codes. If this element is used, then any `Language` elements used in the same `TrackEntry` MUST be ignored.¶

###### 5.1.4.1.21. CodecID Element

id / type:
  0x86 / string¶
path:
  `\Segment\Tracks\TrackEntry\CodecID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  An ID corresponding to the codec; see [MatroskaCodec] for more info.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.22. CodecPrivate Element

id / type:
  0x63A2 / binary¶
path:
  `\Segment\Tracks\TrackEntry\CodecPrivate`¶
maxOccurs:
  1¶
definition:
  Private data only known to the codec.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.23. CodecName Element

id / type:
  0x258688 / utf-8¶
path:
  `\Segment\Tracks\TrackEntry\CodecName`¶
maxOccurs:
  1¶
definition:
  A human-readable string specifying the codec.¶

###### 5.1.4.1.24. AttachmentLink Element

id / type:
  0x7446 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\AttachmentLink`¶
maxOccurs:
  1¶
maxver:
  3¶
definition:
  The UID of an attachment that is used by this codec.¶
usage notes:
  The value MUST match the `FileUID` value of an attachment found in this `Segment`.¶

###### 5.1.4.1.25. CodecDelay Element

id / type / default:
  0x56AA / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\CodecDelay`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  The built-in delay for the codec, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1. It represents the number of codec samples that will be discarded by the decoder during playback. This timestamp value MUST be subtracted from each frame timestamp in order to get the timestamp that will be actually played. The value SHOULD be small so the muxing of tracks with the same actual timestamp are in the same `Cluster`.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.26. SeekPreRoll Element

id / type / default:
  0x56BB / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\SeekPreRoll`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  After a discontinuity, the duration of the data that the decoder MUST decode before the decoded data is valid, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.27. TrackTranslate Element

id / type:
  0x6624 / master¶
path:
  `\Segment\Tracks\TrackEntry\TrackTranslate`¶
definition:
  The mapping between this `TrackEntry` and a track value in the given Chapter Codec.¶
rationale:
  Chapter Codecs may need to address content in a specific track, but they may not know of the way to identify tracks in Matroska. This element and its child elements add a way to map the internal tracks known to the Chapter Codec to the track IDs in Matroska. This allows remuxing a file with Chapter Codec without changing the content of the codec data, just the track mapping.¶

###### 5.1.4.1.27.1. TrackTranslateTrackID Element

id / type:
  0x66A5 / binary¶
path:
  `\Segment\Tracks\TrackEntry\TrackTranslate\TrackTranslateTrackID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The binary value used to represent this `TrackEntry` in the chapter codec data. The format depends on the `ChapProcessCodecID` used; see Section 5.1.7.1.4.15.¶

###### 5.1.4.1.27.2. TrackTranslateCodec Element

id / type:
  0x66BF / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\TrackTranslate\TrackTranslateCodec`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Applies to the chapter codec of the given chapter edition(s); see Section 5.1.7.1.4.15.¶
defined values:
  See Table 31. Additional values can be registered in the "Matroska Chapter Codec IDs" registry defined in Section 27.14.¶

###### 5.1.4.1.27.3. TrackTranslateEditionUID Element

id / type:
  0x66FC / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\TrackTranslate\TrackTranslateEditionUID`¶
definition:
  Specifies a chapter edition UID to which this `TrackTranslate` applies.¶
usage notes:
  When no `TrackTranslateEditionUID` is specified in the `TrackTranslate`, the `TrackTranslate` applies to all chapter editions found in the `Segment` using the given `TrackTranslateCodec`.¶

###### 5.1.4.1.28. Video Element

id / type:
  0xE0 / master¶
path:
  `\Segment\Tracks\TrackEntry\Video`¶
maxOccurs:
  1¶
definition:
  Video settings.¶

###### 5.1.4.1.28.1. FlagInterlaced Element

id / type / default:
  0x9A / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\FlagInterlaced`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  2¶
definition:
  Specifies whether the video frames in this track are interlaced.¶
restrictions:
  See Table 3.¶
stream copy:
  True (Section 8)¶

Table 3: FlagInterlaced Values
value | label | definition
--- | --- | ---
`0` | undetermined | Unknown status. This value SHOULD be avoided.
`1` | interlaced | Interlaced frames.
`2` | progressive | No interlacing.

###### 5.1.4.1.28.2. FieldOrder Element

id / type / default:
  0x9D / uinteger / 2¶
path:
  `\Segment\Tracks\TrackEntry\Video\FieldOrder`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Specifies the field ordering of video frames in this track.¶
restrictions:
  See Table 4.¶
usage notes:
  If `FlagInterlaced` is not set to 1, this element MUST be ignored.¶
stream copy:
  True (Section 8)¶

Table 4: FieldOrder Values
value | label | definition
--- | --- | ---
`0` | progressive | Interlaced frames. This value SHOULD be avoided; setting `FlagInterlaced` to 2 is sufficient.
`1` | tff | Top field displayed first. Top field stored first.
`2` | undetermined | Unknown field order. This value SHOULD be avoided.
`6` | bff | Bottom field displayed first. Bottom field stored first.
`9` | tff (interleaved) | Top field displayed first. Fields are interleaved in storage with the top line of the top field stored first.
`14` | bff (interleaved) | Bottom field displayed first. Fields are interleaved in storage with the top line of the top field stored first.

###### 5.1.4.1.28.3. StereoMode Element

id / type / default:
  0x53B8 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\StereoMode`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  3¶
definition:
  Stereo-3D video mode. See Section 18.10 for more details.¶
defined values:
  See Table 5. Additional values can be registered in the "Matroska Stereo Modes" registry defined in Section 27.7.¶
stream copy:
  True (Section 8)¶

Table 5: StereoMode Values
value | label
--- | ---
`0` | mono
`1` | side by side (left eye first)
`2` | top - bottom (right eye is first)
`3` | top - bottom (left eye is first)
`4` | checkboard (right eye is first)
`5` | checkboard (left eye is first)
`6` | row interleaved (right eye is first)
`7` | row interleaved (left eye is first)
`8` | column interleaved (right eye is first)
`9` | column interleaved (left eye is first)
`10` | anaglyph (cyan/red)
`11` | side by side (right eye first)
`12` | anaglyph (green/magenta)
`13` | both eyes laced in one Block (left eye is first)
`14` | both eyes laced in one Block (right eye is first)

###### 5.1.4.1.28.4. AlphaMode Element

id / type / default:
  0x53C0 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\AlphaMode`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  3¶
definition:
  Indicates whether the `BlockAdditional` element with `BlockAddID` of "1" contains Alpha data as defined by the Codec Mapping for the `CodecID`. Undefined values (i.e., values other than 0 or 1) SHOULD NOT be used, as the behavior of known implementations is different.¶
defined values:
  See Table 6. Additional values can be registered in the "Matroska Alpha Modes" registry defined in Section 27.8.¶
stream copy:
  True (Section 8)¶

Table 6: AlphaMode Values
value | label | definition
--- | --- | ---
`0` | none | The `BlockAdditional` element with `BlockAddID` of "1" does not exist or SHOULD NOT be considered as containing such data.
`1` | present | The `BlockAdditional` element with `BlockAddID` of "1" contains alpha channel data.

###### 5.1.4.1.28.5. OldStereoMode Element

id / type:
  0x53B9 / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\OldStereoMode`¶
maxOccurs:
  1¶
maxver:
  2¶
definition:
  Bogus `StereoMode` value used in old versions of [libmatroska].¶
restrictions:
  See Table 7.¶
usage notes:
  This element MUST NOT be used. It was an incorrect value used in libmatroska up to 0.9.0.¶

Table 7: OldStereoMode Values
value | label
--- | ---
`0` | mono
`1` | right eye
`2` | left eye
`3` | both eyes

###### 5.1.4.1.28.6. PixelWidth Element

id / type:
  0xB0 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\Video\PixelWidth`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Width of the encoded video frames in pixels.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.7. PixelHeight Element

id / type:
  0xBA / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\Video\PixelHeight`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Height of the encoded video frames in pixels.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.8. PixelCropBottom Element

id / type / default:
  0x54AA / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\PixelCropBottom`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The number of video pixels to remove at the bottom of the image.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.9. PixelCropTop Element

id / type / default:
  0x54BB / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\PixelCropTop`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The number of video pixels to remove at the top of the image.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.10. PixelCropLeft Element

id / type / default:
  0x54CC / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\PixelCropLeft`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The number of video pixels to remove on the left of the image.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.11. PixelCropRight Element

id / type / default:
  0x54DD / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\PixelCropRight`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The number of video pixels to remove on the right of the image.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.12. DisplayWidth Element

id / type:
  0x54B0 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\Video\DisplayWidth`¶
maxOccurs:
  1¶
definition:
  Width of the video frames to display. Applies to the video frame after cropping (PixelCrop* Elements).¶
notes:
  See Table 8.¶
stream copy:
  True (Section 8)¶

Table 8: DisplayWidth Implementation Notes
attribute | note
--- | ---
default | If the DisplayUnit of the same `TrackEntry` is 0, then the default value for `DisplayWidth` is equal to `PixelWidth` - `PixelCropLeft` - `PixelCropRight`; else, there is no default value.

###### 5.1.4.1.28.13. DisplayHeight Element

id / type:
  0x54BA / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\Video\DisplayHeight`¶
maxOccurs:
  1¶
definition:
  Height of the video frames to display. Applies to the video frame after cropping (PixelCrop* Elements).¶
notes:
  See Table 9.¶
stream copy:
  True (Section 8)¶

Table 9: DisplayHeight Implementation Notes
attribute | note
--- | ---
default | If the DisplayUnit of the same `TrackEntry` is 0, then the default value for `DisplayHeight` is equal to `PixelHeight` - `PixelCropTop` - `PixelCropBottom`; else, there is no default value.

###### 5.1.4.1.28.14. DisplayUnit Element

id / type / default:
  0x54B2 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\DisplayUnit`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  How `DisplayWidth` and `DisplayHeight` are interpreted.¶
defined values:
  See Table 10. Additional values can be registered in the "Matroska Display Units" registry defined in Section 27.9.¶

Table 10: DisplayUnit Values
value | label
--- | ---
`0` | pixels
`1` | centimeters
`2` | inches
`3` | display aspect ratio
`4` | unknown

###### 5.1.4.1.28.15. UncompressedFourCC Element

id / type:
  0x2EB524 / binary¶
length:
  4¶
path:
  `\Segment\Tracks\TrackEntry\Video\UncompressedFourCC`¶
minOccurs / maxOccurs:
  See Table 11 / 1¶
definition:
  Specifies the uncompressed pixel format used for the `Track`'s data as a FourCC. This value is similar in scope to the biCompression value of AVI's `BITMAPINFO` [AVIFormat]. There is neither a definitive list of FourCC values nor an official registry. Some common values for YUV pixel formats can be found at [MSYUV8], [MSYUV16], and [FourCC-YUV]. Some common values for uncompressed RGB pixel formats can be found at [MSRGB] and [FourCC-RGB].¶
notes:
  See Table 11.¶
stream copy:
  True (Section 8)¶

Table 11: UncompressedFourCC Implementation Notes
attribute | note
--- | ---
minOccurs | UncompressedFourCC MUST be set (minOccurs=1) in `TrackEntry` when the `CodecID` element of the `TrackEntry` is set to "V_UNCOMPRESSED".

###### 5.1.4.1.28.16. Colour Element

id / type:
  0x55B0 / master¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Settings describing the color format.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.17. MatrixCoefficients Element

id / type / default:
  0x55B1 / uinteger / 2¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MatrixCoefficients`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  The Matrix Coefficients of the video used to derive luma and chroma values from red, green, and blue color primaries. For clarity, the value and meanings for `MatrixCoefficients` are adopted from Table 4 of [ITU-H.273].¶
restrictions:
  See Table 12.¶
stream copy:
  True (Section 8)¶

Table 12: MatrixCoefficients Values
value | label
--- | ---
`0` | Identity
`1` | ITU-R BT.709
`2` | unspecified
`3` | reserved
`4` | US FCC 73.682
`5` | ITU-R BT.470BG
`6` | SMPTE 170M
`7` | SMPTE 240M
`8` | YCoCg
`9` | BT2020 Non-constant Luminance
`10` | BT2020 Constant Luminance
`11` | SMPTE ST 2085
`12` | Chroma-derived Non-constant Luminance
`13` | Chroma-derived Constant Luminance
`14` | ITU-R BT.2100-0

###### 5.1.4.1.28.18. BitsPerChannel Element

id / type / default:
  0x55B2 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\BitsPerChannel`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Number of decoded bits per channel. A value of 0 indicates that the `BitsPerChannel` is unspecified.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.19. ChromaSubsamplingHorz Element

id / type:
  0x55B3 / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\ChromaSubsamplingHorz`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The number of pixels to remove in the Cr and Cb channels for every pixel not removed horizontally. Example: For video with 4:2:0 chroma subsampling, the `ChromaSubsamplingHorz` SHOULD be set to 1.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.20. ChromaSubsamplingVert Element

id / type:
  0x55B4 / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\ChromaSubsamplingVert`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The number of pixels to remove in the Cr and Cb channels for every pixel not removed vertically. Example: For video with 4:2:0 chroma subsampling, the `ChromaSubsamplingVert` SHOULD be set to 1.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.21. CbSubsamplingHorz Element

id / type:
  0x55B5 / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\CbSubsamplingHorz`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The number of pixels to remove in the Cb channel for every pixel not removed horizontally. This is additive with `ChromaSubsamplingHorz`. Example: For video with 4:2:1 chroma subsampling, the `ChromaSubsamplingHorz` SHOULD be set to 1, and `CbSubsamplingHorz` SHOULD be set to 1.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.22. CbSubsamplingVert Element

id / type:
  0x55B6 / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\CbSubsamplingVert`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The number of pixels to remove in the Cb channel for every pixel not removed vertically. This is additive with `ChromaSubsamplingVert`.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.23. ChromaSitingHorz Element

id / type / default:
  0x55B7 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\ChromaSitingHorz`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  How chroma is subsampled horizontally.¶
defined values:
  See Table 13. Additional values can be registered in the "Matroska Horizontal Chroma Sitings" registry defined in Section 27.10.¶
stream copy:
  True (Section 8)¶

Table 13: ChromaSitingHorz Values
value | label
--- | ---
`0` | unspecified
`1` | left collocated
`2` | half

###### 5.1.4.1.28.24. ChromaSitingVert Element

id / type / default:
  0x55B8 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\ChromaSitingVert`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  How chroma is subsampled vertically.¶
defined values:
  See Table 14. Additional values can be registered in the "Matroska Vertical Chroma Sitings" registry defined in Section 27.11.¶
stream copy:
  True (Section 8)¶

Table 14: ChromaSitingVert Values
value | label
--- | ---
`0` | unspecified
`1` | top collocated
`2` | half

###### 5.1.4.1.28.25. Color Range Element

id / type / default:
  0x55B9 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\Range`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Clipping of the color ranges.¶
defined values:
  See Table 15. Additional values can be registered in the "Matroska Color Ranges" registry defined in Section 27.12.¶
stream copy:
  True (Section 8)¶

Table 15: Range Values
value | label
--- | ---
`0` | unspecified
`1` | broadcast range
`2` | full range (no clipping)
`3` | defined by MatrixCoefficients / TransferCharacteristics

###### 5.1.4.1.28.26. TransferCharacteristics Element

id / type / default:
  0x55BA / uinteger / 2¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\TransferCharacteristics`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  The transfer characteristics of the video. For clarity, the value and meanings for `TransferCharacteristics` are adopted from Table 3 of [ITU-H.273].¶
restrictions:
  See Table 16.¶
stream copy:
  True (Section 8)¶

Table 16: TransferCharacteristics Values
value | label
--- | ---
`0` | reserved
`1` | ITU-R BT.709
`2` | unspecified
`3` | reserved2
`4` | Gamma 2.2 curve - BT.470M
`5` | Gamma 2.8 curve - BT.470BG
`6` | SMPTE 170M
`7` | SMPTE 240M
`8` | Linear
`9` | Log
`10` | Log Sqrt
`11` | IEC 61966-2-4
`12` | ITU-R BT.1361 Extended Colour Gamut
`13` | IEC 61966-2-1
`14` | ITU-R BT.2020 10 bit
`15` | ITU-R BT.2020 12 bit
`16` | ITU-R BT.2100 Perceptual Quantization
`17` | SMPTE ST 428-1
`18` | ARIB STD-B67 (HLG)

###### 5.1.4.1.28.27. Primaries Element

id / type / default:
  0x55BB / uinteger / 2¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\Primaries`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  The color primaries of the video. For clarity, the value and meanings for `Primaries` are adopted from Table 2 of [ITU-H.273].¶
restrictions:
  See Table 17.¶
stream copy:
  True (Section 8)¶

Table 17: Primaries Values
value | label
--- | ---
`0` | reserved
`1` | ITU-R BT.709
`2` | unspecified
`3` | reserved2
`4` | ITU-R BT.470M
`5` | ITU-R BT.470BG - BT.601 625
`6` | ITU-R BT.601 525 - SMPTE 170M
`7` | SMPTE 240M
`8` | FILM
`9` | ITU-R BT.2020
`10` | SMPTE ST 428-1
`11` | SMPTE RP 432-2
`12` | SMPTE EG 432-2
`22` | EBU Tech. 3213-E - JEDEC P22 phosphors

###### 5.1.4.1.28.28. MaxCLL Element

id / type:
  0x55BC / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MaxCLL`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Maximum brightness of a single pixel (Maximum Content Light Level) in candelas per square meter (cd/m2).¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.29. MaxFALL Element

id / type:
  0x55BD / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MaxFALL`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Maximum brightness of a single full frame (Maximum Frame-Average Light Level) in candelas per square meter (cd/m2).¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.30. MasteringMetadata Element

id / type:
  0x55D0 / master¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  SMPTE 2086 mastering data.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.31. PrimaryRChromaticityX Element

id / type:
  0x55D1 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryRChromaticityX`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Red X chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.32. PrimaryRChromaticityY Element

id / type:
  0x55D2 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryRChromaticityY`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Red Y chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.33. PrimaryGChromaticityX Element

id / type:
  0x55D3 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryGChromaticityX`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Green X chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.34. PrimaryGChromaticityY Element

id / type:
  0x55D4 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryGChromaticityY`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Green Y chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.35. PrimaryBChromaticityX Element

id / type:
  0x55D5 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryBChromaticityX`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Blue X chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.36. PrimaryBChromaticityY Element

id / type:
  0x55D6 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\PrimaryBChromaticityY`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Blue Y chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.37. WhitePointChromaticityX Element

id / type:
  0x55D7 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\WhitePointChromaticityX`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  White X chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.38. WhitePointChromaticityY Element

id / type:
  0x55D8 / float¶
range:
  0x0p+0-0x1p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\WhitePointChromaticityY`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  White Y chromaticity coordinate, as defined by [CIE-1931].¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.39. LuminanceMax Element

id / type:
  0x55D9 / float¶
range:
  >= 0x0p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\LuminanceMax`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Maximum luminance. Represented in candelas per square meter (cd/m2).¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.40. LuminanceMin Element

id / type:
  0x55DA / float¶
range:
  >= 0x0p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Colour\MasteringMetadata\LuminanceMin`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Minimum luminance. Represented in candelas per square meter (cd/m2).¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.41. Projection Element

id / type:
  0x7670 / master¶
path:
  `\Segment\Tracks\TrackEntry\Video\Projection`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Describes the video projection details. Used to render spherical or VR videos or to flip videos horizontally or vertically.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.42. ProjectionType Element

id / type / default:
  0x7671 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Projection\ProjectionType`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Describes the projection used for this video track.¶
defined values:
  See Table 18. Additional values can be registered in the "Matroska Projection Types" registry defined in Section 27.15.¶
stream copy:
  True (Section 8)¶

Table 18: ProjectionType Values
value | label
--- | ---
`0` | rectangular
`1` | equirectangular
`2` | cubemap
`3` | mesh

###### 5.1.4.1.28.43. ProjectionPrivate Element

id / type:
  0x7672 / binary¶
path:
  `\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPrivate`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Private data that only applies to a specific projection.¶

- If `ProjectionType` equals 0 (rectangular), then this element MUST NOT be present.¶
- If `ProjectionType` equals 1 (equirectangular), then this element MUST be present and contain the same binary data that would be stored inside an ISOBMFF Equirectangular Projection Box ("equi").¶
- If `ProjectionType` equals 2 (cubemap), then this element MUST be present and contain the same binary data that would be stored inside an ISOBMFF Cubemap Projection Box ("cbmp").¶
- If `ProjectionType` equals 3 (mesh), then this element MUST be present and contain the same binary data that would be stored inside an ISOBMFF Mesh Projection Box ("mshp").¶

usage notes:
  ISOBMFF box size and FourCC fields are not included in the binary data, but the FullBox version and flag fields are. This is to avoid redundant framing information while preserving versioning and semantics between the two container formats.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.44. ProjectionPoseYaw Element

id / type / default:
  0x7673 / float / 0x0p+0¶
range:
  >= -0xB4p+0, <= 0xB4p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPoseYaw`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Specifies a yaw rotation to the projection. Value represents a clockwise rotation, in degrees, around the up vector. This rotation must be applied before any `ProjectionPosePitch` or `ProjectionPoseRoll` rotations. The value of this element MUST be in the -180 to 180 degree range, both inclusive.¶

Setting `ProjectionPoseYaw` to 180 or -180 degrees with `ProjectionPoseRoll` and `ProjectionPosePitch` set to 0 degrees flips the image horizontally.¶

stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.45. ProjectionPosePitch Element

id / type / default:
  0x7674 / float / 0x0p+0¶
range:
  >= -0x5Ap+0, <= 0x5Ap+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPosePitch`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Specifies a pitch rotation to the projection. Value represents a counter-clockwise rotation, in degrees, around the right vector. This rotation must be applied after the `ProjectionPoseYaw` rotation and before the `ProjectionPoseRoll` rotation. The value of this element MUST be in the -90 to 90 degree range, both inclusive.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.28.46. ProjectionPoseRoll Element

id / type / default:
  0x7675 / float / 0x0p+0¶
range:
  >= -0xB4p+0, <= 0xB4p+0¶
path:
  `\Segment\Tracks\TrackEntry\Video\Projection\ProjectionPoseRoll`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  Specifies a roll rotation to the projection. Value represents a counter-clockwise rotation, in degrees, around the forward vector. This rotation must be applied after the `ProjectionPoseYaw` and `ProjectionPosePitch` rotations. The value of this element MUST be in the -180 to 180 degree range, both inclusive. Setting `ProjectionPoseRoll` to 180 or -180 degrees and `ProjectionPoseYaw` to 180 or -180 degrees with `ProjectionPosePitch` set to 0 degrees flips the image vertically. Setting `ProjectionPoseRoll` to 180 or -180 degrees with `ProjectionPoseYaw` and `ProjectionPosePitch` set to 0 degrees flips the image horizontally and vertically.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.29. Audio Element

id / type:
  0xE1 / master¶
path:
  `\Segment\Tracks\TrackEntry\Audio`¶
maxOccurs:
  1¶
definition:
  Audio settings.¶

###### 5.1.4.1.29.1. SamplingFrequency Element

id / type / default:
  0xB5 / float / 0x1.f4p+12¶
range:
  > 0x0p+0¶
path:
  `\Segment\Tracks\TrackEntry\Audio\SamplingFrequency`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Sampling frequency in Hz.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.29.2. OutputSamplingFrequency Element

id / type:
  0x78B5 / float¶
range:
  > 0x0p+0¶
path:
  `\Segment\Tracks\TrackEntry\Audio\OutputSamplingFrequency`¶
maxOccurs:
  1¶
definition:
  Real output sampling frequency in Hz that is used for Spectral Band Replication (SBR) techniques.¶
notes:
  See Table 19.¶

Table 19: OutputSamplingFrequency Implementation Notes
attribute | note
--- | ---
default | The default value for `OutputSamplingFrequency` of the same `TrackEntry` is equal to the `SamplingFrequency`.

###### 5.1.4.1.29.3. Channels Element

id / type / default:
  0x9F / uinteger / 1¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\Audio\Channels`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Numbers of channels in the track.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.29.4. BitDepth Element

id / type:
  0x6264 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\Audio\BitDepth`¶
maxOccurs:
  1¶
definition:
  Bits per sample, mostly used for PCM.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.30. TrackOperation Element

id / type:
  0xE2 / master¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation`¶
maxOccurs:
  1¶
minver:
  3¶
definition:
  Operation that needs to be applied on tracks to create this virtual track. For more details, see Section 18.8.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.30.1. TrackCombinePlanes Element

id / type:
  0xE3 / master¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes`¶
maxOccurs:
  1¶
minver:
  3¶
definition:
  Contains the list of all video plane tracks that need to be combined to create this 3D track.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.30.2. TrackPlane Element

id / type:
  0xE4 / master¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes\TrackPlane`¶
minOccurs:
  1¶
minver:
  3¶
definition:
  Contains a video plane track that needs to be combined to create this 3D track.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.30.3. TrackPlaneUID Element

id / type:
  0xE5 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes\TrackPlane\TrackPlaneUID`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  3¶
definition:
  The `TrackUID` number of the track representing the plane.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.30.4. TrackPlaneType Element

id / type:
  0xE6 / uinteger¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation\TrackCombinePlanes\TrackPlane\TrackPlaneType`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  3¶
definition:
  The kind of plane this track corresponds to.¶
defined values:
  See Table 20. Additional values can be registered in the "Matroska Track Plane Types" registry defined in Section 27.17.¶
stream copy:
  True (Section 8)¶

Table 20: TrackPlaneType Values
value | label
--- | ---
`0` | left eye
`1` | right eye
`2` | background

###### 5.1.4.1.30.5. TrackJoinBlocks Element

id / type:
  0xE9 / master¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation\TrackJoinBlocks`¶
maxOccurs:
  1¶
minver:
  3¶
definition:
  Contains the list of all tracks whose `Blocks` need to be combined to create this virtual track.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.30.6. TrackJoinUID Element

id / type:
  0xED / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\TrackOperation\TrackJoinBlocks\TrackJoinUID`¶
minOccurs:
  1¶
minver:
  3¶
definition:
  The `TrackUID` number of a track whose blocks are used to create this virtual track.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31. ContentEncodings Element

id / type:
  0x6D80 / master¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings`¶
maxOccurs:
  1¶
definition:
  Settings for several content encoding mechanisms like compression or encryption.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.1. ContentEncoding Element

id / type:
  0x6240 / master¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding`¶
minOccurs:
  1¶
definition:
  Settings for one content encoding like compression or encryption.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.2. ContentEncodingOrder Element

id / type / default:
  0x5031 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncodingOrder`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Defines the order to apply each `ContentEncoding` of the `ContentEncodings`. The decoder/demuxer MUST start with the `ContentEncoding` with the highest `ContentEncodingOrder` and work its way down to the `ContentEncoding` with the lowest `ContentEncodingOrder`. This value MUST be unique for each `ContentEncoding` found in the `ContentEncodings` of this `TrackEntry`.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.3. ContentEncodingScope Element

id / type / default:
  0x5032 / uinteger / 1¶
range:
  not 0 (0x1-0x8000000000000000)¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncodingScope`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  A bit field that describes which elements have been modified in this way. Values (big-endian) can be OR'ed.¶
defined values:
  See Table 21. Additional values can be registered in the "Matroska Content Encoding Scopes" registry defined in Section 27.5.¶
stream copy:
  True (Section 8)¶

Table 21: ContentEncodingScope Values
value | label | definition
--- | --- | ---
`0x1` | Block | All frame contents, excluding lacing data.
`0x2` | Private | The track's `CodecPrivate` data.
`0x4` | Next | The next ContentEncoding (next `ContentEncodingOrder`; the data inside `ContentCompression` and/or `ContentEncryption`). This value SHOULD NOT be used, as it's not supported by players.

###### 5.1.4.1.31.4. ContentEncodingType Element

id / type / default:
  0x5033 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncodingType`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  A value describing the kind of transformation that is applied.¶
defined values:
  See Table 22. Additional values can be registered in the "Matroska Content Encoding Types" registry defined in Section 27.6.¶
stream copy:
  True (Section 8)¶

Table 22: ContentEncodingType Values
value | label
--- | ---
`0` | Compression
`1` | Encryption

###### 5.1.4.1.31.5. ContentCompression Element

id / type:
  0x5034 / master¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentCompression`¶
maxOccurs:
  1¶
definition:
  Settings describing the compression used. This element MUST be present if the value of `ContentEncodingType` is 0 and absent otherwise. Each block MUST be decompressable, even if no previous block is available in order to not prevent seeking.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.6. ContentCompAlgo Element

id / type / default:
  0x4254 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentCompression\ContentCompAlgo`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The compression algorithm used.¶
defined values:
  See Table 23. Additional values can be registered in the "Matroska Compression Algorithms" registry defined in Section 27.2.¶
usage notes:
  Compression method "1" (bzlib) and "2" (lzo1x) lack proper documentation on the format, which limits implementation possibilities. Due to licensing conflicts on commonly available libraries' compression methods, "2" (lzo1x) does not offer widespread interoperability. A `Matroska Writer` SHOULD NOT use these compression methods by default. A `Matroska Reader` MAY support methods "1" and "2" and SHOULD support other methods.¶
stream copy:
  True (Section 8)¶

Table 23: ContentCompAlgo Values
value | label | definition
--- | --- | ---
`0` | zlib | zlib compression [RFC1950].
`1` | bzlib | bzip2 compression [BZIP2] SHOULD NOT be used; see usage notes.
`2` | lzo1x | Lempel-Ziv-Oberhumer compression [LZO] SHOULD NOT be used; see usage notes.
`3` | Header Stripping | Octets in `ContentCompSettings` (Section 5.1.4.1.31.7) have been stripped from each frame.

###### 5.1.4.1.31.7. ContentCompSettings Element

id / type:
  0x4255 / binary¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentCompression\ContentCompSettings`¶
maxOccurs:
  1¶
definition:
  Settings that might be needed by the decompressor. For Header Stripping (`ContentCompAlgo`=3), the bytes that were removed from the beginning of each frame of the track.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.8. ContentEncryption Element

id / type:
  0x5035 / master¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption`¶
maxOccurs:
  1¶
definition:
  Settings describing the encryption used. This element MUST be present if the value of `ContentEncodingType` is 1 (encryption) and MUST be ignored otherwise. A `Matroska Player` MAY support encryption.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.9. ContentEncAlgo Element

id / type / default:
  0x47E1 / uinteger / 0¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncAlgo`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The encryption algorithm used.¶
defined values:
  See Table 24. Additional values can be registered in the "Matroska Encryption Algorithms" registry defined in Section 27.3.¶
stream copy:
  True (Section 8)¶

Table 24: ContentEncAlgo Values
value | label | definition
--- | --- | ---
`0` | Not encrypted | The data are not encrypted.
`1` | DES | Data Encryption Standard (DES) [FIPS46-3]. This value SHOULD be avoided.
`2` | 3DES | Triple Data Encryption Algorithm [SP800-67]. This value SHOULD be avoided.
`3` | Twofish | Twofish Encryption Algorithm [Twofish].
`4` | Blowfish | Blowfish Encryption Algorithm [Blowfish]. This value SHOULD be avoided.
`5` | AES | Advanced Encryption Standard (AES) [FIPS197].

###### 5.1.4.1.31.10. ContentEncKeyID Element

id / type:
  0x47E2 / binary¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncKeyID`¶
maxOccurs:
  1¶
definition:
  For public key algorithms, the ID of the public key that the data was encrypted with.¶
stream copy:
  True (Section 8)¶

###### 5.1.4.1.31.11. ContentEncAESSettings Element

id / type:
  0x47E7 / master¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncAESSettings`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  Settings describing the encryption algorithm used.¶
notes:
  See Table 25.¶
stream copy:
  True (Section 8)¶

Table 25: ContentEncAESSettings Implementation Notes
attribute | note
--- | ---
maxOccurs | ContentEncAESSettings MUST NOT be set (maxOccurs=0) if ContentEncAlgo is not AES (5).

###### 5.1.4.1.31.12. AESSettingsCipherMode Element

id / type:
  0x47E8 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentEncAESSettings\AESSettingsCipherMode`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  4¶
definition:
  The AES cipher mode used in the encryption.¶
defined values:
  See Table 26. Additional values can be registered in the "Matroska AES Cipher Modes" registry defined in Section 27.4.¶
notes:
  See Table 27.¶
stream copy:
  True (Section 8)¶

Table 26: AESSettingsCipherMode Values
value | label | definition
--- | --- | ---
`1` | AES-CTR | Counter [SP800-38A]
`2` | AES-CBC | Cipher Block Chaining [SP800-38A]

Table 27: AESSettingsCipherMode Implementation Notes
attribute | note
--- | ---
maxOccurs | AESSettingsCipherMode MUST NOT be set (maxOccurs=0) if ContentEncAlgo is not AES (5).

#### 5.1.5. Cues Element

id / type:
  0x1C53BB6B / master¶
path:
  `\Segment\Cues`¶
minOccurs / maxOccurs:
  See Table 28 / 1¶
definition:
  A `Top-Level Element` to speed seeking access. All entries are local to the `Segment`.¶
notes:
  See Table 28.¶

Table 28: Cues Implementation Notes
attribute | note
--- | ---
minOccurs | This element SHOULD be set when the `Segment` is not transmitted as a live stream; see Section 23.2.

##### 5.1.5.1. CuePoint Element

id / type:
  0xBB / master¶
path:
  `\Segment\Cues\CuePoint`¶
minOccurs:
  1¶
definition:
  Contains all information relative to a seek point in the `Segment`.¶

###### 5.1.5.1.1. CueTime Element

id / type:
  0xB3 / uinteger¶
path:
  `\Segment\Cues\CuePoint\CueTime`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Absolute timestamp of the seek point, expressed in Segment Ticks, which are based on `TimestampScale`; see Section 11.1.¶

###### 5.1.5.1.2. CueTrackPositions Element

id / type:
  0xB7 / master¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions`¶
minOccurs:
  1¶
definition:
  Contains positions for different tracks corresponding to the timestamp.¶

###### 5.1.5.1.2.1. CueTrack Element

id / type:
  0xF7 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueTrack`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The track for which a position is given.¶

###### 5.1.5.1.2.2. CueClusterPosition Element

id / type:
  0xF1 / uinteger¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueClusterPosition`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The `Segment Position` (Section 16) of the `Cluster` containing the associated `Block`.¶

###### 5.1.5.1.2.3. CueRelativePosition Element

id / type:
  0xF0 / uinteger¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueRelativePosition`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The relative position inside the `Cluster` of the referenced `SimpleBlock` or `BlockGroup` with 0 being the first possible position for an element inside that `Cluster`.¶

###### 5.1.5.1.2.4. CueDuration Element

id / type:
  0xB2 / uinteger¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueDuration`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The duration of the block, expressed in Segment Ticks, which are based on `TimestampScale`; see Section 11.1. If missing, the track's `DefaultDuration` does not apply and no duration information is available in terms of the cues.¶

###### 5.1.5.1.2.5. CueBlockNumber Element

id / type:
  0x5378 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueBlockNumber`¶
maxOccurs:
  1¶
definition:
  Number of the `Block` in the specified `Cluster`.¶

###### 5.1.5.1.2.6. CueCodecState Element

id / type / default:
  0xEA / uinteger / 0¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueCodecState`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  2¶
definition:
  The `Segment Position` (Section 16) of the Codec State corresponding to this `Cues` element. 0 means that the data is taken from the initial `TrackEntry`.¶

###### 5.1.5.1.2.7. CueReference Element

id / type:
  0xDB / master¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueReference`¶
minver:
  2¶
definition:
  The `Clusters` containing the referenced `Blocks`.¶

###### 5.1.5.1.2.8. CueRefTime Element

id / type:
  0x96 / uinteger¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefTime`¶
minOccurs / maxOccurs:
  1 / 1¶
minver:
  2¶
definition:
  Timestamp of the referenced `Block`, expressed in Segment Ticks which is based on `TimestampScale`; see Section 11.1.¶

#### 5.1.6. Attachments Element

id / type:
  0x1941A469 / master¶
path:
  `\Segment\Attachments`¶
maxOccurs:
  1¶
definition:
  Contains attached files.¶

##### 5.1.6.1. AttachedFile Element

id / type:
  0x61A7 / master¶
path:
  `\Segment\Attachments\AttachedFile`¶
minOccurs:
  1¶
definition:
  An attached file.¶

###### 5.1.6.1.1. FileDescription Element

id / type:
  0x467E / utf-8¶
path:
  `\Segment\Attachments\AttachedFile\FileDescription`¶
maxOccurs:
  1¶
definition:
  A human-friendly name for the attached file.¶

###### 5.1.6.1.2. FileName Element

id / type:
  0x466E / utf-8¶
path:
  `\Segment\Attachments\AttachedFile\FileName`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Filename of the attached file.¶

###### 5.1.6.1.3. FileMediaType Element

id / type:
  0x4660 / string¶
path:
  `\Segment\Attachments\AttachedFile\FileMediaType`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Media type of the file following the format described in [RFC6838].¶
stream copy:
  True (Section 8)¶

###### 5.1.6.1.4. FileData Element

id / type:
  0x465C / binary¶
path:
  `\Segment\Attachments\AttachedFile\FileData`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The data of the file.¶
stream copy:
  True (Section 8)¶

###### 5.1.6.1.5. FileUID Element

id / type:
  0x46AE / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Attachments\AttachedFile\FileUID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  UID representing the file, as random as possible.¶
stream copy:
  True (Section 8)¶

#### 5.1.7. Chapters Element

id / type:
  0x1043A770 / master¶
path:
  `\Segment\Chapters`¶
maxOccurs:
  1¶
recurring:
  True¶
definition:
  A system to define basic menus and partition data. For more detailed information, see Section 20.¶

##### 5.1.7.1. EditionEntry Element

id / type:
  0x45B9 / master¶
path:
  `\Segment\Chapters\EditionEntry`¶
minOccurs:
  1¶
definition:
  Contains all information about a `Segment` edition.¶

###### 5.1.7.1.1. EditionUID Element

id / type:
  0x45BC / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Chapters\EditionEntry\EditionUID`¶
maxOccurs:
  1¶
definition:
  A UID that identifies the edition. It's useful for tagging an edition.¶
stream copy:
  True (Section 8)¶

###### 5.1.7.1.2. EditionFlagDefault Element

id / type / default:
  0x45DB / uinteger / 0¶
range:
  0-1¶
path:
  `\Segment\Chapters\EditionEntry\EditionFlagDefault`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Set to 1 if the edition SHOULD be used as the default one.¶

###### 5.1.7.1.3. EditionFlagOrdered Element

id / type / default:
  0x45DD / uinteger / 0¶
range:
  0-1¶
path:
  `\Segment\Chapters\EditionEntry\EditionFlagOrdered`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Set to 1 if the chapters can be defined multiple times and the order to play them is enforced; see Section 20.1.3.¶

###### 5.1.7.1.4. ChapterAtom Element

id / type:
  0xB6 / master¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom`¶
minOccurs:
  1¶
recursive:
  True¶
definition:
  Contains the atom information to use as the chapter atom (applies to all tracks).¶

###### 5.1.7.1.4.1. ChapterUID Element

id / type:
  0x73C4 / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterUID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  A UID that identifies the `Chapter`.¶
stream copy:
  True (Section 8)¶

###### 5.1.7.1.4.2. ChapterStringUID Element

id / type:
  0x5654 / utf-8¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterStringUID`¶
maxOccurs:
  1¶
minver:
  3¶
definition:
  A unique string ID that identifies the `Chapter`. For example, it is used as the storage for cue identifier values [WebVTT].¶

###### 5.1.7.1.4.3. ChapterTimeStart Element

id / type:
  0x91 / uinteger¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterTimeStart`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Timestamp of the start of `Chapter`, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1.¶

###### 5.1.7.1.4.4. ChapterTimeEnd Element

id / type:
  0x92 / uinteger¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterTimeEnd`¶
minOccurs / maxOccurs:
  See Table 29 / 1¶
definition:
  Timestamp of the end of `Chapter` (timestamp excluded), expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1. The value MUST be greater than or equal to the `ChapterTimeStart` of the same `ChapterAtom`.¶
usage notes:
  With the `ChapterTimeEnd` timestamp value being excluded, it MUST take into account the duration of the last frame it includes, especially for the `ChapterAtom` using the last frames of the `Segment`.¶
notes:
  See Table 29.¶

Table 29: ChapterTimeEnd Implementation Notes
attribute | note
--- | ---
minOccurs | ChapterTimeEnd MUST be set (minOccurs=1) if the `Edition` is an ordered edition; see Section 20.1.3. If it's a `Parent Chapter`, see Section 20.2.3.

###### 5.1.7.1.4.5. ChapterFlagHidden Element

id / type / default:
  0x98 / uinteger / 0¶
range:
  0-1¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterFlagHidden`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Set to 1 if a chapter is hidden. Hidden chapters SHOULD NOT be available to the user interface (but still be available to Control Tracks; see Section 20.2.5 on `Chapter` flags).¶

###### 5.1.7.1.4.6. ChapterSegmentUUID Element

id / type:
  0x6E67 / binary¶
length:
  16¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterSegmentUUID`¶
minOccurs / maxOccurs:
  See Table 30 / 1¶
definition:
  The `SegmentUUID` of another `Segment` to play during this chapter.¶
usage notes:
  The value MUST NOT be the `SegmentUUID` value of the `Segment` it belongs to.¶
notes:
  See Table 30.¶

Table 30: ChapterSegmentUUID Implementation Notes
attribute | note
--- | ---
minOccurs | `ChapterSegmentUUID` MUST be set (minOccurs=1) if `ChapterSegmentEditionUID` is used; see Section 17.2 on Medium-Linking `Segments`.

###### 5.1.7.1.4.7. ChapterSegmentEditionUID Element

id / type:
  0x6EBC / uinteger¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterSegmentEditionUID`¶
maxOccurs:
  1¶
definition:
  The `EditionUID` to play from the `Segment` linked in `ChapterSegmentUUID`. If `ChapterSegmentEditionUID` is undeclared, then no `Edition` of the `Linked Segment` is used; see Section 17.2 on Medium-Linking `Segments`.¶

###### 5.1.7.1.4.8. ChapterPhysicalEquiv Element

id / type:
  0x63C3 / uinteger¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterPhysicalEquiv`¶
maxOccurs:
  1¶
definition:
  Specifies the physical equivalent of this `ChapterAtom`, e.g., "DVD" (60) or "SIDE" (50); see Section 20.4 for a complete list of values.¶

###### 5.1.7.1.4.9. ChapterDisplay Element

id / type:
  0x80 / master¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay`¶
definition:
  Contains all possible strings to use for the chapter display.¶

###### 5.1.7.1.4.10. ChapString Element

id / type:
  0x85 / utf-8¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapString`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Contains the string to use as the chapter atom.¶

###### 5.1.7.1.4.11. ChapLanguage Element

id / type / default:
  0x437C / string / eng¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapLanguage`¶
minOccurs:
  1¶
definition:
  A language corresponding to the string, in the Matroska languages form; see Section 12 on language codes. This element MUST be ignored if a `ChapLanguageBCP47` element is used within the same `ChapterDisplay` element.¶

###### 5.1.7.1.4.12. ChapLanguageBCP47 Element

id / type:
  0x437D / string¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapLanguageBCP47`¶
minver:
  4¶
definition:
  A language corresponding to the `ChapString`, in the form defined in [RFC5646]; see Section 12 on language codes. If a `ChapLanguageBCP47` element is used, then any `ChapLanguage` and `ChapCountry` elements used in the same `ChapterDisplay` MUST be ignored.¶

###### 5.1.7.1.4.13. ChapCountry Element

id / type:
  0x437E / string¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapterDisplay\ChapCountry`¶
definition:
  A country corresponding to the string, in the Matroska countries form; see Section 13 on country codes. This element MUST be ignored if a `ChapLanguageBCP47` element is used within the same `ChapterDisplay` element.¶

###### 5.1.7.1.4.14. ChapProcess Element

id / type:
  0x6944 / master¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess`¶
definition:
  Contains all the commands associated with the Atom.¶

###### 5.1.7.1.4.15. ChapProcessCodecID Element

id / type / default:
  0x6955 / uinteger / 0¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCodecID`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Contains the type of the codec used for processing.¶
defined values:
  See Table 31. Additional values can be registered in the "Matroska Chapter Codec IDs" registry defined in Section 27.14.¶

Table 31: ChapProcessCodecID Values
value | label | definition
--- | --- | ---
`0` | Matroska Script | Chapter commands using the Matroska Script codec.
`1` | DVD-menu | Chapter commands using the DVD-like codec.

###### 5.1.7.1.4.16. ChapProcessPrivate Element

id / type:
  0x450D / binary¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessPrivate`¶
maxOccurs:
  1¶
definition:
  Optional data attached to the `ChapProcessCodecID` information. For `ChapProcessCodecID` = 1, it is the "DVD level" equivalent; see Section 20.3 on DVD menus.¶

###### 5.1.7.1.4.17. ChapProcessCommand Element

id / type:
  0x6911 / master¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCommand`¶
definition:
  Contains all the commands associated with the Atom.¶

###### 5.1.7.1.4.18. ChapProcessTime Element

id / type:
  0x6922 / uinteger¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCommand\ChapProcessTime`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Defines when the process command SHOULD be handled.¶
restrictions:
  See Table 32.¶

Table 32: ChapProcessTime Values
value | label
--- | ---
`0` | during the whole chapter
`1` | before starting playback
`2` | after playback of the chapter

###### 5.1.7.1.4.19. ChapProcessData Element

id / type:
  0x6933 / binary¶
path:
  `\Segment\Chapters\EditionEntry\+ChapterAtom\ChapProcess\ChapProcessCommand\ChapProcessData`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Contains the command information. The data SHOULD be interpreted depending on the `ChapProcessCodecID` value. For `ChapProcessCodecID` = 1, the data correspond to the binary DVD cell pre/post commands; see Section 20.3 on DVD menus.¶

#### 5.1.8. Tags Element

id / type:
  0x1254C367 / master¶
path:
  `\Segment\Tags`¶
definition:
  Element containing metadata describing `Tracks`, `Editions`, `Chapters`, `Attachments`, or the `Segment` as a whole. A list of valid tags can be found in [MatroskaTags].¶

##### 5.1.8.1. Tag Element

id / type:
  0x7373 / master¶
path:
  `\Segment\Tags\Tag`¶
minOccurs:
  1¶
definition:
  A single metadata descriptor.¶

###### 5.1.8.1.1. Targets Element

id / type:
  0x63C0 / master¶
path:
  `\Segment\Tags\Tag\Targets`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Specifies which other elements the metadata represented by the tag value applies to. If empty or omitted, then the tag value describes everything in the `Segment`.¶

###### 5.1.8.1.1.1. TargetTypeValue Element

id / type / default:
  0x68CA / uinteger / 50¶
range:
  not 0 (1-18446744073709551615)¶
path:
  `\Segment\Tags\Tag\Targets\TargetTypeValue`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  A number to indicate the logical level of the target.¶
defined values:
  See Table 33. Additional values can be registered in the "Matroska Tags Target Types" registry defined in Section 27.13.¶
usage notes:
  The `TargetTypeValue` values are meant to be compared. Higher values MUST correspond to a logical level that contains the lower logical level `TargetTypeValue` values.¶

Table 33: TargetTypeValue Values
value | label | definition
--- | --- | ---
`70` | COLLECTION | The highest hierarchical level that tags can describe.
`60` | EDITION / ISSUE / VOLUME / OPUS / SEASON / SEQUEL | A list of lower levels grouped together.
`50` | ALBUM / OPERA / CONCERT / MOVIE / EPISODE | The most common grouping level of music and video (e.g., an episode for TV series).
`40` | PART / SESSION | When an album or episode has different logical parts.
`30` | TRACK / SONG / CHAPTER | The common parts of an album or movie.
`20` | SUBTRACK / MOVEMENT / SCENE | Corresponds to parts of a track for audio, such as a movement or scene in a movie.
`10` | SHOT | The lowest hierarchy found in music or movies.

###### 5.1.8.1.1.2. TargetType Element

id / type:
  0x63CA / string¶
path:
  `\Segment\Tags\Tag\Targets\TargetType`¶
maxOccurs:
  1¶
definition:
  An informational string that can be used to display the logical level of the target, such as "ALBUM", "TRACK", "MOVIE", "CHAPTER", etc.¶
restrictions:
  See Table 34.¶

Table 34: TargetType Values
value | label
--- | ---
`COLLECTION` | TargetTypeValue 70
`EDITION` | TargetTypeValue 60
`ISSUE` | TargetTypeValue 60
`VOLUME` | TargetTypeValue 60
`OPUS` | TargetTypeValue 60
`SEASON` | TargetTypeValue 60
`SEQUEL` | TargetTypeValue 60
`ALBUM` | TargetTypeValue 50
`OPERA` | TargetTypeValue 50
`CONCERT` | TargetTypeValue 50
`MOVIE` | TargetTypeValue 50
`EPISODE` | TargetTypeValue 50
`PART` | TargetTypeValue 40
`SESSION` | TargetTypeValue 40
`TRACK` | TargetTypeValue 30
`SONG` | TargetTypeValue 30
`CHAPTER` | TargetTypeValue 30
`SUBTRACK` | TargetTypeValue 20
`MOVEMENT` | TargetTypeValue 20
`SCENE` | TargetTypeValue 20
`SHOT` | TargetTypeValue 10

###### 5.1.8.1.1.3. TagTrackUID Element

id / type / default:
  0x63C5 / uinteger / 0¶
path:
  `\Segment\Tags\Tag\Targets\TagTrackUID`¶
definition:
  A UID that identifies the `Track(s)` that the tags belong to.¶
usage notes:
  If the value is 0 at this level, the tags apply to all tracks in the `Segment`. If set to any other value, it MUST match the `TrackUID` value of a track found in this `Segment`.¶

###### 5.1.8.1.1.4. TagEditionUID Element

id / type / default:
  0x63C9 / uinteger / 0¶
path:
  `\Segment\Tags\Tag\Targets\TagEditionUID`¶
definition:
  A UID that identifies the `EditionEntry(s)` that the tags belong to.¶
usage notes:
  If the value is 0 at this level, the tags apply to all editions in the `Segment`. If set to any other value, it MUST match the `EditionUID` value of an edition found in this `Segment`.¶

###### 5.1.8.1.1.5. TagChapterUID Element

id / type / default:
  0x63C4 / uinteger / 0¶
path:
  `\Segment\Tags\Tag\Targets\TagChapterUID`¶
definition:
  A UID that identifies the `Chapter(s)` that the tags belong to.¶
usage notes:
  If the value is 0 at this level, the tags apply to all chapters in the `Segment`. If set to any other value, it MUST match the `ChapterUID` value of a chapter found in this `Segment`.¶

###### 5.1.8.1.1.6. TagAttachmentUID Element

id / type / default:
  0x63C6 / uinteger / 0¶
path:
  `\Segment\Tags\Tag\Targets\TagAttachmentUID`¶
definition:
  A UID that identifies the Attachment(s) that the tags belong to.¶
usage notes:
  If the value is 0 at this level, the tags apply to all the attachments in the `Segment`. If set to any other value, it MUST match the `FileUID` value of an attachment found in this `Segment`.¶

###### 5.1.8.1.2. SimpleTag Element

id / type:
  0x67C8 / master¶
path:
  `\Segment\Tags\Tag\+SimpleTag`¶
minOccurs:
  1¶
recursive:
  True¶
definition:
  Contains general information about the target.¶

###### 5.1.8.1.2.1. TagName Element

id / type:
  0x45A3 / utf-8¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagName`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  The name of the tag value that is going to be stored.¶

###### 5.1.8.1.2.2. TagLanguage Element

id / type / default:
  0x447A / string / und¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagLanguage`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  Specifies the language of the specified tag in the Matroska languages form; see Section 12 on language codes. This element MUST be ignored if the `TagLanguageBCP47` element is used within the same `SimpleTag` element.¶

###### 5.1.8.1.2.3. TagLanguageBCP47 Element

id / type:
  0x447B / string¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagLanguageBCP47`¶
maxOccurs:
  1¶
minver:
  4¶
definition:
  The language used in the `TagString`, in the form defined in [RFC5646]; see Section 12 on language codes. If this element is used, then any `TagLanguage` elements used in the same `SimpleTag` MUST be ignored.¶

###### 5.1.8.1.2.4. TagDefault Element

id / type / default:
  0x4484 / uinteger / 1¶
range:
  0-1¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagDefault`¶
minOccurs / maxOccurs:
  1 / 1¶
definition:
  A boolean value to indicate if this is the default/original language to use for the given tag.¶

###### 5.1.8.1.2.5. TagString Element

id / type:
  0x4487 / utf-8¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagString`¶
maxOccurs:
  1¶
definition:
  The tag value.¶

###### 5.1.8.1.2.6. TagBinary Element

id / type:
  0x4485 / binary¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagBinary`¶
maxOccurs:
  1¶
definition:
  The tag value if it is binary. Note that this cannot be used in the same `SimpleTag` as `TagString`.¶

## 6. Matroska Element Ordering

With the exceptions of the `EBML Header` and the `CRC-32` element, the EBML specification [RFC8794] does not require any particular storage order for elements. However, this specification defines mandates and recommendations for ordering certain elements to facilitate better playback, seeking, and editing efficiency. This section describes and offers rationale for ordering requirements and recommendations for Matroska.¶

### 6.1. Top-Level Elements

The `Info` element is the only REQUIRED `Top-Level Element` in a Matroska file. To be playable, Matroska MUST also contain at least one `Tracks` element and `Cluster` element. The first `Info` element and the first `Tracks` element either MUST be stored before the first `Cluster` element or SHALL both be referenced by a `SeekHead` element occurring before the first `Cluster` element.¶

All `Top-Level Elements` MUST use a 4-octet EBML Element ID.¶

When using Medium Linking, chapters are used to reference other `Segments` to play in a given order (see Section 17.2). A `Segment` containing these `Linked Chapters` does not require a `Tracks` element or a `Cluster` element.¶

It is possible to edit a Matroska file after it has been created. For example, chapters, tags, or attachments can be added. When new `Top-Level Elements` are added to a Matroska file, the `SeekHead` element(s) MUST be updated so that the `SeekHead` element(s) itemizes the identity and position of all `Top-Level Elements`.¶

Editing, removing, or adding elements to a Matroska file often requires that some existing elements be voided or extended. Transforming the existing elements into `Void` elements as padding can be used as a method to avoid moving large amounts of data around.¶

### 6.2. CRC-32

As noted by the EBML specification [RFC8794], if a `CRC-32` element is used, then the `CRC-32` element MUST be the first ordered element within its `Parent Element`.¶

In Matroska, all `Top-Level Elements` of an EBML Document SHOULD include a `CRC-32` element as their first `Child Element`. The `Segment` element, which is the `Root Element`, SHOULD NOT have a `CRC-32` element.¶

### 6.3. SeekHead

If used, the first `SeekHead` element MUST be the first non-`CRC-32 Child` element of the `Segment` element. If a second `SeekHead` element is used, then the first `SeekHead` element MUST reference the identity and position of the second `SeekHead` element.¶

Additionally, the second `SeekHead` element MUST only reference `Cluster` elements and not any other `Top-Level Element` already contained within the first `SeekHead` element.¶

The second `SeekHead` element MAY be stored in any order relative to the other `Top-Level Elements`. Whether one or two `SeekHead` elements are used, the `SeekHead` element(s) MUST collectively reference the identity and position of all `Top-Level Elements` except for the first `SeekHead` element.¶

### 6.4. Cues (Index)

The `Cues` element is RECOMMENDED to optimize seeking access in Matroska. It is programmatically simpler to add the `Cues` element after all `Cluster` elements have been written because this does not require a prediction of how much space to reserve before writing the `Cluster` elements. However, storing the `Cues` element before the `Cluster` elements can provide some seeking advantages. If the `Cues` element is present, then it SHOULD either be stored before the first `Cluster` element or be referenced by a `SeekHead` element.¶

### 6.5. Info

The first `Info` element SHOULD occur before the first `Tracks` element and first `Cluster` element except when referenced by a `SeekHead` element.¶

### 6.6. Chapters Element

The `Chapters` element SHOULD be placed before the `Cluster` element(s). The `Chapters` element can be used during playback even if the user does not need to seek. It immediately gives the user information about what section is being read and what other sections are available.¶

In the case of `Ordered Chapters`, it is RECOMMENDED to evaluate the logical linking before playing. The `Chapters` element SHOULD be placed before the first `Tracks` element and after the first `Info` element.¶

### 6.7. Attachments

The `Attachments` element is not intended to be used by default when playing the file but could contain information relevant to the content, such as cover art or fonts. Cover art is useful even before the file is played, and fonts could be needed before playback starts for the initialization of subtitles. The `Attachments` element MAY be placed before the first `Cluster` element; however, if the `Attachments` element is likely to be edited, then it SHOULD be placed after the last `Cluster` element.¶

### 6.8. Tags

The `Tags` element is most subject to changes after the file was originally created. For easier editing, the `Tags` element can be placed at the end of the `Segment` element, even after the `Attachments` element. On the other hand, it is inconvenient to have to seek in the `Segment` for tags, especially for network streams; thus, it's better if the `Tags` element is found early in the stream. When editing the `Tags` element, the original `Tags` element at the beginning can be overwritten with a `Void` element and a new `Tags` element written at the end of the `Segment` element. The file and `Segment` sizes will only marginally change.¶

## 7. Matroska Versioning

Matroska is based on the principle that a reading application does not have to support 100% of the specifications in order to be able to play the file. Therefore, a Matroska file contains version indicators that tell a reading application what to expect.¶

It is possible and valid to have the version fields indicate that the file contains Matroska elements from a higher specification version number while signaling that a reading application MUST only support a lower version number properly in order to play it back (possibly with a reduced feature set).¶

The `EBML Header` of each Matroska document informs the reading application on what version of Matroska to expect. The elements within the `EBML Header` with jurisdiction over this information are `DocTypeVersion` and `DocTypeReadVersion`.¶

`DocTypeVersion` MUST be equal to or greater than the highest Matroska version number of any element present in the Matroska file. For example, a file using the `SimpleBlock` element (Section 5.1.3.4) MUST have a `DocTypeVersion` equal to or greater than 2. A file containing `CueRelativePosition` elements (Section 5.1.5.1.2.3) MUST have a `DocTypeVersion` equal to or greater than 4.¶

The `DocTypeReadVersion` MUST contain the minimum version number that a reading application can minimally support in order to play the file back -- optionally with a reduced feature set. For example, if a file contains only elements of version 2 or lower except for `CueRelativePosition` (which is a version 4 Matroska element), then `DocTypeReadVersion` SHOULD still be set to 2 and not 4 because evaluating `CueRelativePosition` is not necessary for standard playback -- it makes seeking more precise if used.¶

A reading application supporting Matroska version `V` MUST NOT refuse to read a file with `DocReadTypeVersion` equal to or lower than `V`, even if `DocTypeVersion` is greater than `V`.¶

A reading application supporting at least Matroska version `V` and reading a file whose `DocTypeReadVersion` field is equal to or lower than `V` MUST skip Matroska/EBML elements it encounters but does not know about if that unknown element fits into the size constraints set by the current `Parent Element`.¶

## 8. Stream Copy

It is sometimes necessary to create a Matroska file from another Matroska file, for example, to add subtitles in a language or to edit out a portion of the content. Some values from the original Matroska file need to be kept the same in the destination file. For example, the `SamplingFrequency` of an audio track wouldn't change between the two files. Some other values may change between the two files, for example, the `TrackNumber` of an audio track when another track has been added.¶

An element is marked with a property "`stream copy: True`" when the values of that element need to be kept identical between the source and destination files. If that property is not set, elements may or may not keep the same value between the source and destination files.¶

## 9. DefaultDecodedFieldDuration

The `DefaultDecodedFieldDuration` element can signal to the displaying application how often fields of a video sequence will be available for displaying. It can be used for both interlaced and progressive content.¶

If the video sequence is signaled as interlaced (Section 5.1.4.1.28.1), then `DefaultDecodedFieldDuration` equals the period between two successive fields at the output of the decoding process. For video sequences signaled as progressive, `DefaultDecodedFieldDuration` is half of the period between two successive frames at the output of the decoding process.¶

These values are valid at the end of the decoding process before post-processing (such as deinterlacing or inverse telecine) is applied.¶

Examples:¶

- Blu-ray movie: 1000000000 ns/(48/1.001) = 20854167 ns¶

- PAL broadcast/DVD: 1000000000 ns/(50/1.000) = 20000000 ns¶

- N/ATSC broadcast: 1000000000 ns/(60/1.001) = 16683333 ns¶

- Hard-telecined DVD: 1000000000 ns/(60/1.001) = 16683333 ns (60 encoded interlaced fields per second)¶

- Soft-telecined DVD: 1000000000 ns/(60/1.001) = 16683333 ns (48 encoded interlaced fields per second, with "repeat_first_field = 1")¶

## 10. Cluster Blocks

Frames using references SHOULD be stored in "coding order" (i.e., the references first and then the frames referencing them). A consequence is that timestamps might not be consecutive. However, a frame with a past timestamp MUST reference a frame already known; otherwise, it is considered bad/void.¶

Matroska has two similar ways to store frames in a block:¶

- in a `Block` that is contained inside a `BlockGroup`¶

- in a `SimpleBlock` that is directly in the `Cluster`¶

The `SimpleBlock` is usually preferred unless some extra elements of the `BlockGroup` need to be used. A `Matroska Reader` MUST support both types of blocks.¶

Each block contains the same parts in the following order:¶

- a variable-length header¶

- the lacing information (optional)¶

- the consecutive frame(s)¶

The block header starts with the number of the `Track` it corresponds to. The value MUST correspond to the `TrackNumber` (Section 5.1.4.1.1) of a `TrackEntry` of the `Segment`.¶

The `TrackNumber` is coded using the Variable-Size Integer (VINT) mechanism described in Section 4 of [RFC8794]. To save space, the shortest VINT form SHOULD be used. The value can be coded using up to 8 octets. This is the only element with a variable size in the block header.¶

The timestamp is expressed in Track Ticks; see Section 11.1. The value is stored as a signed value on 16 bits.¶

### 10.1. Block Structure

This section describes the binary data contained in the `Block` element (Section 5.1.3.5.1). Bit 0 is the most significant bit.¶

As the `TrackNumber` size can vary between 1 and 8 octets, there are 8 different sizes for the `Block` header. The definitions for `TrackNumber` sizes of 1 and 2 are provided; the other variants can be deduced by extending the size of the `TrackNumber` by multiples of 8 bits.¶

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               |                               |       |I|LAC|U|
     |  Track Number |         Timestamp             | Rsvrd |N|ING|N|
     |               |                               |       |V|   |U|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11: Block Header with 1-Octet TrackNumber

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Track Number         |         Timestamp             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       |I|LAC|U|
     | Rsvrd |N|ING|N|                     ...
     |       |V|   |U|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 12: Block Header with 2-Octet TrackNumber

where:¶

Track Number:
  8, 16, 24, 32, 40, 48, or 56 bits. An EBML VINT-coded track number.¶
Timestamp:
  16 bits. Signed timestamp in Track Ticks.¶
Rsvrd:
  4 bits. Reserved bits MUST be set to 0.¶
INV:
  1 bit. Invisible; The codec SHOULD decode this frame but not display it.¶
LACING:

  2 bits. Uses lacing mode.¶

  00b:
    no lacing (Section 10.3.1)¶
  01b:
    Xiph lacing (Section 10.3.2)¶
  11b:
    EBML lacing (Section 10.3.3)¶
  10b:
    fixed-size lacing (Section 10.3.4)¶
UNU:
  1 bit. Unused bit.¶

The remaining data in the `Block` corresponds to the lacing data and frames usage as described in each respective lacing mode (see Section 10.3).¶

### 10.2. SimpleBlock Structure

This section describes the binary data contained in the `SimpleBlock` element (Section 5.1.3.4). Bit 0 is the most significant bit.¶

The `SimpleBlock` structure is inspired by the `Block` structure; see Section 10.1. The main differences are the added Keyframe flag and Discardable flag. Otherwise, everything is the same.¶

As the `TrackNumber` size can vary between 1 and 8 octets, there are 8 different sizes for the `SimpleBlock` header. The definitions for `TrackNumber` sizes of 1 and 2 are provided; the other variants can be deduced by extending the size of the `TrackNumber` by multiples of 8 bits.¶

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               |                               |K|     |I|LAC|D|
     |  Track Number |         Timestamp             |E|Rsvrd|N|ING|I|
     |               |                               |Y|     |V|   |S|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 13: SimpleBlock Header with 1-Octet TrackNumber

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Track Number         |         Timestamp             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |K|     |I|LAC|D|
     |E|Rsvrd|N|ING|I|                     ...
     |Y|     |V|   |S|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14: SimpleBlock Header with 2-Octet TrackNumber

where:¶

Track Number:
  8, 16, 24, 32, 40, 48, or 56 bits. An EBML VINT-coded track number.¶
Timestamp:
  16 bits. Signed timestamp in Track Ticks.¶
KEY:
  1 bit. Keyframe; Set when the `Block` contains only keyframes.¶
Rsvrd:
  3 bits. Reserved bits MUST be set to 0.¶
INV:
  1 bit. Invisible; the codec SHOULD decode this frame but not display it.¶
LACING:

  2 bits. Uses lacing mode.¶

  00b:
    no lacing (Section 10.3.1)¶
  01b:
    Xiph lacing (Section 10.3.2)¶
  11b:
    EBML lacing (Section 10.3.3)¶
  10b:
    fixed-size lacing (Section 10.3.4)¶
DIS:
  1 bit. Discardable; The frames of the `Block` can be discarded during playing if needed.¶

The remaining data in the `SimpleBlock` corresponds to the lacing data and frames usage as described in each respective lacing mode (see Section 10.3).¶

### 10.3. Block Lacing

Lacing is a mechanism to save space when storing data. It is typically used for small blocks of data (referred to as frames in Matroska). It packs multiple frames into a single `Block` or `SimpleBlock`.¶

Lacing MUST NOT be used to store a single frame in a `Block` or `SimpleBlock`.¶

There are three types of lacing:¶

- Xiph, which is inspired by what is found in the Ogg container [RFC3533]¶

- EBML, which is the same with sizes coded differently¶

- Fixed-size, where the size is not coded¶

When lacing is not used, i.e., to store a single frame, the lacing bits (bits 5 and 6) of the `Block` or `SimpleBlock` MUST be set to zero.¶

For example, a user wants to store three frames of the same track. The first frame is 800 octets long, the second is 500 octets long, and the third is 1000 octets long. Because these frames are small, they can be stored in a lace to save space.¶

It is possible to not use lacing at all and just store a single frame without any extra data. When the `FlagLacing` (Section 5.1.4.1.12) is set to 0, all blocks of that track MUST NOT use lacing.¶

#### 10.3.1. No Lacing

When no lacing is used, the number of frames in the lace is omitted, and only one frame can be stored in the `Block`. The LACING bits of the `Block` Header flags are set to `00b`.¶

The `Block` for an 800-octet frame is as follows:¶

Table 35: No Lacing
Block Octet | Value | Description
--- | --- | ---
4-803 | <frame> | Single frame data

When a `Block` contains a single frame, it MUST use this "no lacing" mode.¶

#### 10.3.2. Xiph Lacing

The Xiph lacing uses the same coding of size as found in the Ogg container [RFC3533]. The LACING bits of the `Block` Header flags are set to `01b`.¶

The `Block` data with laced frames is stored as follows:¶

- Lacing Head on 1 Octet: Number of frames in the lace minus 1.¶

- Lacing size of each frame except the last one.¶

- Binary data of each frame consecutively.¶

The lacing size is split into 255 values, stored as unsigned octets -- for example, 500 is coded 255;245 or [0xFF 0xF5]. A frame with a size multiple of 255 is coded with a 0 at the end of the size -- for example, 765 is coded 255;255;255;0 or [0xFF 0xFF 0xFF 0x00].¶

The size of the last frame is deduced from the size remaining in the `Block` after the other frames.¶

Because large sizes result in large coding of the sizes, it is RECOMMENDED to use Xiph lacing only with small frames.¶

In our example, the 800-, 500-, and 1000-octet frames are stored with Xiph lacing in a `Block` as follows:¶

Table 36: Xiph Lacing Example
Block Octets | Value | Description
--- | --- | ---
4 | 0x02 | Number of frames minus 1
5-8 | 0xFF 0xFF 0xFF 0x23 | Size of the first frame (255;255;255;35)
9-10 | 0xFF 0xF5 | Size of the second frame (255;245)
11-810 |  | First frame data
811-1310 |  | Second frame data
1311-2310 |  | Third frame data

The `Block` is 2311 octets, and the last frame starts at 1311, so we can deduce that the size of the last frame is 2311 - 1311 = 1000.¶

#### 10.3.3. EBML Lacing

The EBML lacing encodes the frame size with an EBML-like encoding [RFC8794]. The LACING bits of the `Block` Header flags are set to `11b`.¶

The `Block` data with laced frames is stored as follows:¶

- Lacing Head on 1 Octet: Number of frames in the lace minus 1.¶

- Lacing size of each frame except the last one.¶

- Binary data of each frame consecutively.¶

The first frame size is encoded as an EBML VINT value. The remaining frame sizes are encoded as signed values using the difference between the frame size and the previous frame size. These signed values are encoded as VINT, with a mapping from signed to unsigned numbers. Decoding the unsigned number stored in the VINT to a signed number is done by subtracting 2((7*n)-1)-1, where `n` is the octet size of the VINT.¶

Table 37: EBML Lacing Signed VINT Bits Usage
Bit Representation of Signed VINT | Possible Value Range
--- | ---
1xxx xxxx | 2^7 values from -(26-1) to 26
01xx xxxx xxxx xxxx | 2^14 values from -(213-1) to 213
001x xxxx xxxx xxxx xxxx xxxx | 2^21 values from -(220-1) to 220
0001 xxxx xxxx xxxx xxxx xxxx xxxx xxxx | 2^28 values from -(227-1) to 227
0000 1xxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx | 2^35 values from -(234-1) to 234

In our example, the 800-, 500-, and 1000-octet frames are stored with EBML lacing in a `Block` as follows:¶

Table 38: EBML Lacing Example
Block Octets | Value | Description
--- | --- | ---
4 | 0x02 | Number of frames minus 1
5-6 | 0x43 0x20 | Size of the first frame (800 = 0x320 + 0x4000)
7-8 | 0x5E 0xD3 | Size of the second frame (500 - 800 = -300 = - 0x12C + 0x1FFF + 0x4000)
8-807 | <frame1> | First frame data
808-1307 | <frame2> | Second frame data
1308-2307 | <frame3> | Third frame data

The `Block` is 2308 octets, and the last frame starts at 1308, so we can deduce that the size of the last frame is 2308 - 1308 = 1000.¶

#### 10.3.4. Fixed-size Lacing

Fixed-size lacing doesn't store the frame size; rather, it only stores the number of frames in the lace. Each frame MUST have the same size. The frame size of each frame is deduced from the total size of the `Block`. The LACING bits of the `Block` Header flags are set to `10b`.¶

The `Block` data with laced frames is stored as follows:¶

- Lacing Head on 1 Octet: Number of frames in the lace minus 1.¶

- Binary data of each frame consecutively.¶

For example, for three frames that are 800 octets each:¶

Table 39: Fixed-Size Lacing Example
Block Octets | Value | Description
--- | --- | ---
4 | 0x02 | Number of frames minus 1
5-804 | <frame1> | First frame data
805-1604 | <frame2> | Second frame data
1605-2404 | <frame3> | Third frame data

This gives a `Block` of 2405 octets. When reading the `Block`, we find that there are three frames (Octet 4). The data start at Octet 5, so the size of each frame is (2405 - 5) / 3 = 800.¶

#### 10.3.5. Laced Frames Timestamp

A `Block` only contains a single timestamp value. But when lacing is used, it contains more than one frame. Each frame originally has its own timestamp, or Presentation Timestamp (PTS). That timestamp applies to the first frame in the lace.¶

In the lace, each frame after the first one has an underdetermined timestamp. However, each of these frames MUST be contiguous -- i.e., the decoded data MUST NOT contain any gap between them. If there is a gap in the stream, the frames around the gap MUST NOT be in the same `Block`.¶

Lacing is only useful for small contiguous data to save space. This is usually the case for audio tracks and not the case for video (which use a lot of data) or subtitle tracks (which have long gaps). For audio, there is usually a fixed output sampling frequency for the whole track, so the decoder should be able to recover the timestamp of each sample, knowing each output sample is contiguous with a fixed frequency. For subtitles, this is usually not the case, so lacing SHOULD NOT be used.¶

### 10.4. Random Access Points

Random Access Points (RAPs) are positions where the parser can seek to and start playback without decoding what was before. In Matroska, `BlockGroups` and `SimpleBlocks` can be RAPs. To seek to these elements, it is still necessary to seek to the `Cluster` containing them, read the `Cluster` Timestamp, and start playback from the `BlockGroup` or `SimpleBlock` that is a RAP.¶

Because a Matroska File is usually composed of multiple tracks playing at the same time -- video, audio, and subtitles -- to seek properly to a RAP, each selected track must be taken into account. Usually, all audio and subtitle `BlockGroups` or `SimpleBlocks` are RAPs. They are independent of each other and can be played randomly.¶

On the other hand, video tracks often use references to previous and future frames for better coding efficiency. Frames with such references MUST either contain one or more `ReferenceBlock` elements in their `BlockGroup` or MUST be marked as non-keyframe in a `SimpleBlock`; see Section 10.2.¶

    <Cluster>
      <Timestamp>123456</Timestamp>
      <BlockGroup>
        <!-- References a Block 40 Track Ticks before this one -->
        <ReferenceBlock>-40</ReferenceBlock>
        <Block/>
      </BlockGroup>
      ...
    </Cluster>

Figure 15: BlockGroup with a Frame That References Another Frame, with the EBML Tree Shown as XML

    <Cluster>
      <Timestamp>123456</Timestamp>
      <SimpleBlock/> (octet 3 bit 0 not set)
      ...
    </Cluster>

Figure 16: SimpleBlock with a Frame That References Another Frame, with the EBML Tree Shown as XML

Frames that are RAPs (i.e., frames that don't depend on other frames) MUST set the keyframe flag if they are in a `SimpleBlock` or their parent `BlockGroup` MUST NOT contain a `ReferenceBlock`.¶

    <Cluster>
      <Timestamp>123456</Timestamp>
      <BlockGroup>
        <!-- No ReferenceBlock allowed in this BlockGroup -->
        <Block/>
      </BlockGroup>
      ...
    </Cluster>

Figure 17: BlockGroup with a Frame That References No Other Frame, with the EBML Tree Shown as XML

    <Cluster>
      <Timestamp>123456</Timestamp>
      <SimpleBlock/> (octet 3 bit 0 set)
      ...
    </Cluster>

Figure 18: SimpleBlock with a Frame That References No Other Frame, with the EBML Tree Shown as XML

There may be cases where the use of `BlockGroup` is necessary, as the frame may need a `BlockDuration`, `BlockAdditions`, `CodecState`, or `DiscardPadding` element. For those cases, a `SimpleBlock` MUST NOT be used; the reference information SHOULD be recovered for non-RAP frames.¶

    <Cluster>
      <Timestamp>123456</Timestamp>
      <SimpleBlock/> (octet 3 bit 0 not set)
      ...
    </Cluster>

Figure 19: SimpleBlock with a Frame That References Another Frame, with the EBML Tree Shown as XML

    <Cluster>
      <Timestamp>123456</Timestamp>
      <BlockGroup>
        <!-- ReferenceBlock value recovered based on the codec -->
        <ReferenceBlock>-40</ReferenceBlock>
        <BlockDuration>20</BlockDuration>
        <Block/>
      </BlockGroup>
      ...
    </Cluster>

Figure 20: Same Frame That References Another Frame Put inside a `BlockGroup` to Add `BlockDuration`, with the EBML Tree Shown as XML

When a frame in a `BlockGroup` is not a RAP, the `BlockGroup` MUST contain at least a `ReferenceBlock`. The `ReferenceBlock`s MUST be used in one of the following ways:¶

- each reference frame listed as a `ReferenceBlock`,¶

- some referenced frames listed as a `ReferenceBlock`, even if the timestamp value is accurate, or¶

- one `ReferenceBlock` with the timestamp value "0" corresponding to a self or unknown reference.¶

The lack of `ReferenceBlock` would mean such a frame is a RAP, and seeking on that frame that actually depends on other frames may create a bogus output or even crash.¶

    <Cluster>
      <Timestamp>123456</Timestamp>
      <BlockGroup>
        <!-- ReferenceBlock value not recovered from the codec -->
        <ReferenceBlock>0</ReferenceBlock>
        <BlockDuration>20</BlockDuration>
        <Block/>
      </BlockGroup>
      ...
    </Cluster>

Figure 21: Same Frame That References Another Frame Put inside a `BlockGroup`, but the Reference Could Not Be Recovered, with the EBML Tree Shown as XML

    <Cluster>
      <Timestamp>123456</Timestamp>
      <BlockGroup>
        <!-- References a Block 80 Track Ticks before this one -->
        <ReferenceBlock>-80</ReferenceBlock>
        <!-- References a Block 40 Track Ticks after this one -->
        <ReferenceBlock>40</ReferenceBlock>
        <Block/>
      </BlockGroup>
      ...
    </Cluster>

Figure 22: `BlockGroup` with a Frame That References Two Other Frames, with the EBML Tree Shown as XML

Intra-only video frames, such as the ones found in AV1 or VP9, can be decoded without any other frame, but they don't reset the codec state. Thus, seeking to these frames is not possible, as the next frames may need frames that are not known from this seeking point. Such intra-only frames MUST NOT be considered as keyframes, so the keyframe flag MUST NOT be set in the `SimpleBlock` or a `ReferenceBlock` MUST be used to signify the frame is not a RAP. The timestamp value of the `ReferenceBlock` MUST be "0", meaning it's referencing itself.¶

    <Cluster>
      <Timestamp>123456</Timestamp>
      <BlockGroup>
        <!-- References itself to mark it should not be used as RAP -->
        <ReferenceBlock>0</ReferenceBlock>
        <Block/>
      </BlockGroup>
      ...
    </Cluster>

Figure 23: Intra-Only Frame (Not a RAP), with the EBML Tree Shown as XML

Because a video `SimpleBlock` has less information on references than a video `BlockGroup`, it is possible to remux a video track using `BlockGroup` into a `SimpleBlock`, as long as it doesn't use any other `BlockGroup` features than `ReferenceBlock`.¶

## 11. Timestamps

Historically, timestamps in Matroska were mistakenly called timecodes. The `Timestamp` element was called Timecode, the `TimestampScale` element was called TimecodeScale, the `TrackTimestampScale` element was called TrackTimecodeScale, and the `ReferenceTimestamp` element was called ReferenceTimeCode.¶

### 11.1. Timestamp Ticks

All timestamp values in Matroska are expressed in multiples of a tick. They are usually stored as integers. There are three types of ticks possible: Matroska Ticks, Segment Ticks, and Track Ticks.¶

#### 11.1.1. Matroska Ticks

The timestamp value is stored directly in nanoseconds.¶

The elements storing values in Matroska Ticks/nanoseconds are:¶

- `TrackEntry\DefaultDuration`; defined in Section 5.1.4.1.13¶

- `TrackEntry\DefaultDecodedFieldDuration`; defined in Section 5.1.4.1.14¶

- `TrackEntry\SeekPreRoll`; defined in Section 5.1.4.1.26¶

- `TrackEntry\CodecDelay`; defined in Section 5.1.4.1.25¶

- `BlockGroup\DiscardPadding`; defined in Section 5.1.3.5.7¶

- `ChapterAtom\ChapterTimeStart`; defined in Section 5.1.7.1.4.3¶

- `ChapterAtom\ChapterTimeEnd`; defined in Section 5.1.7.1.4.4¶

#### 11.1.2. Segment Ticks

Elements in Segment Ticks involve the use of the `TimestampScale` element of the `Segment` to get the timestamp in nanoseconds of the element, with the following formula:¶

    timestamp in nanosecond = element value * TimestampScale

¶

This allows for storage of smaller integer values in the elements.¶

When using the default value of "1,000,000" for `TimestampScale`, one Segment Tick represents one millisecond.¶

The elements storing values in Segment Ticks are:¶

- `Cluster\Timestamp`; defined in Section 5.1.3.1¶

- `Info\Duration` is stored as a floating-point, but the same formula applies; defined in Section 5.1.2.10¶

- `CuePoint\CueTime`; defined in Section 5.1.5.1.1¶

- `CuePoint\CueTrackPositions\CueDuration`; defined in Section 5.1.5.1.2.4¶

- `CueReference\CueRefTime`; defined in Section 5.1.5.1.1¶

#### 11.1.3. Track Ticks

Elements in Track Ticks involve the use of the `TimestampScale` element of the `Segment` and the `TrackTimestampScale` element of the `Track` to get the timestamp in nanoseconds of the element, with the following formula:¶

    timestamp in nanoseconds =
        element value * TrackTimestampScale * TimestampScale

¶

This allows for storage of smaller integer values in the elements. The resulting floating-point values of the timestamps are still expressed in nanoseconds.¶

When using the default values of "1,000,000" for `TimestampScale` and "1.0" for `TrackTimestampScale`, one Track Tick represents one millisecond.¶

The elements storing values in Track Ticks are:¶

- `Cluster\BlockGroup\Block` and `Cluster\SimpleBlock` timestamps; detailed in Section 11.2¶

- `Cluster\BlockGroup\BlockDuration`; defined in Section 5.1.3.5.3¶

- `Cluster\BlockGroup\ReferenceBlock`; defined in Section 5.1.3.5.5¶

When the `TrackTimestampScale` is interpreted as "1.0", Track Ticks are equivalent to Segment Ticks and give an integer value in nanoseconds. This is the most common case as `TrackTimestampScale` is usually omitted.¶

A value of `TrackTimestampScale` other than "1.0" MAY be used to scale the timestamps more in tune with each `Track` sampling frequency. For historical reasons, a lot of `Matroska Readers` don't take the `TrackTimestampScale` value into account. Thus, using a value other than "1.0" might not work in many places.¶

### 11.2. Block Timestamps

A `Block` element and `SimpleBlock` element timestamp is the time when the decoded data of the first frame in the `Block`/`SimpleBlock` MUST be presented if the track of that `Block`/`SimpleBlock` is selected for playback. This is also known as the Presentation Timestamp (PTS).¶

The `Block` element and `SimpleBlock` element store their timestamps as signed integers, relative to the `Cluster\Timestamp` value of the `Cluster` they are stored in. To get the timestamp of a `Block` or `SimpleBlock` in nanoseconds, the following formula is used:¶

    ( Cluster\Timestamp + ( block timestamp * TrackTimestampScale ) ) *
    TimestampScale

¶

The `Block` element and `SimpleBlock` element store their timestamps as 16-bit signed integers, allowing a range from "-32768" to "+32767" Track Ticks. Although these values can be negative, when added to the `Cluster\Timestamp`, the resulting frame timestamp SHOULD NOT be negative.¶

When a `CodecDelay` element is set, its value MUST be subtracted from each `Block` timestamp of that track. To get the timestamp in nanoseconds of the first frame in a `Block` or `SimpleBlock`, the formula becomes:¶

    ( ( Cluster\Timestamp + ( block timestamp * TrackTimestampScale ) ) *
      TimestampScale ) - CodecDelay

¶

The resulting frame timestamp SHOULD NOT be negative.¶

During playback, when a frame has a negative timestamp, the content MUST be decoded by the decoder but not played to the user.¶

### 11.3. TimestampScale Rounding

The default Track Tick duration is one millisecond.¶

The `TimestampScale` is a floating-point value that is usually "1.0". But when it's not, the multiplied `Block` Timestamp is a floating-point value in nanoseconds. The `Matroska Reader` SHOULD use the nearest rounding value in nanoseconds to get the proper nanosecond timestamp of a `Block`. This allows some clever `TimestampScale` values to have a more refined timestamp precision per frame.¶

## 12. Language Codes

Matroska versions 1 through 3 use language codes that can be either the three-letter bibliographic ISO 639-2 form [ISO639-2] (like "fre" for French) or such a language code followed by a dash and a country code for specialities in languages (like "fre-ca" for Canadian French). The `ISO 639-2 Language` elements are `Language` element, `TagLanguage` element, and `ChapLanguage` element.¶

Starting in Matroska version 4, the forms defined in either [ISO639-2] or [RFC5646] MAY be used, although the form in [RFC5646] is RECOMMENDED. The `Language` elements in the [RFC5646] form are `LanguageBCP47` element, `TagLanguageBCP47` element, and `ChapLanguageBCP47` element. If both an [ISO639-2] Language element and an [RFC5646] Language element are used within the same `Parent Element`, then the `Language` element in the [ISO639-2] form MUST be ignored and precedence given to the `Language` element in the [RFC5646] form.¶

In this document, "BCP47" in element names refers specifically to [RFC5646], which is part of BCP 47.¶

## 13. Country Codes

Country codes are the [RFC5646] two-letter region subtags, without the UK exception.¶

## 14. Encryption

This Matroska specification provides no interoperable solution for securing the data container with any assurances of confidentiality, integrity, authenticity, or authorization. The `ContentEncryption` element (Section 5.1.4.1.31.8) and associated sub-fields (Section 5.1.4.1.31.9 to Section 5.1.4.1.31.12) are defined only for the benefit of implementers to construct their own proprietary solution or as the basis for further standardization activities. How to use these fields to secure a Matroska data container is out of scope, as are any related issues such as key management and distribution.¶

A `Matroska Reader` who encounters containers that use the fields defined in this section MUST rely on out-of-scope guidance to decode the associated content.¶

Because encryption occurs within the `Block` element, it is possible to manipulate encrypted streams without decrypting them. The streams could potentially be copied, deleted, cut, appended, or any number of other possible editing techniques without decryption. The data can be used without having to expose it or go through the decrypting process.¶

Encryption can also be layered within Matroska. This means that two completely different types of encryption can be used, requiring two separate keys to be able to decrypt a stream.¶

Encryption information is stored in the `ContentEncodings` element under the `ContentEncryption` element.¶

For encryption systems sharing public/private keys, the creation of the keys and the exchange of keys are not covered by this document. They have to be handled by the system using Matroska.¶

The algorithms described in Table 24 support different modes of operations and key sizes. The specification of these parameters is required for a complete solution but is out of scope of this document and left to the proprietary implementations using them or subsequent profiles of this document.¶

The `ContentEncodingScope` element gives an idea of which part of the track is encrypted, but each `ContentEncAlgo` element and its sub-elements (like `AESSettingsCipherMode`) define exactly how the encrypted track should be interpreted.¶

An example of an extension that builds upon these security-related fields in this specification is [WebM-Enc]. It uses AES-CTR, `ContentEncAlgo` = 5 (Section 5.1.4.1.31.9), and `AESSettingsCipherMode` = 1 (Section 5.1.4.1.31.12).¶

A `Matroska Writer` MUST NOT use insecure cryptographic algorithms to create new archives or streams, but a `Matroska Reader` MAY support these algorithms to read previously made archives or streams.¶

## 15. Image Presentation

### 15.1. Cropping

The `PixelCrop` elements (`PixelCropTop`, `PixelCropBottom`, `PixelCropRight`, and `PixelCropLeft`) indicate when, and by how much, encoded video frames SHOULD be cropped for display. These elements allow edges of the frame that are not intended for display (such as the sprockets of a full-frame film scan or the Video ANCillary (VANC) area of a digitized analog videotape) to be stored but hidden. `PixelCropTop` and `PixelCropBottom` store an integer of how many rows of pixels SHOULD be cropped from the top and bottom of the image, respectively. `PixelCropLeft` and `PixelCropRight` store an integer of how many columns of pixels SHOULD be cropped from the left and right of the image, respectively.¶

For example, a pillar-boxed video that stores a 1440x1080 visual image within the center of a padded 1920x1080 encoded image may set both `PixelCropLeft` and `PixelCropRight` to "240", so a `Matroska Player` should crop off 240 columns of pixels from the left and right of the encoded image to present the image with the pillar-boxes hidden.¶

Cropping has to be performed before resizing and the display dimensions given by `DisplayWidth`, `DisplayHeight`, and `DisplayUnit` apply to the already-cropped image.¶

### 15.2. Rotation

The `ProjectionPoseRoll` element (Section 5.1.4.1.28.46) can be used to indicate that the image from the associated video track SHOULD be rotated for presentation. For instance, the following example of the `Projection` element (Section 5.1.4.1.28.41) and the `ProjectionPoseRoll` element represents a video track where the image SHOULD be presented with a 90-degree counter-clockwise rotation, with the EBML tree shown as XML:¶

    <Projection>
      <ProjectionPoseRoll>90</ProjectionPoseRoll>
    </Projection>

Figure 24: Rotation Example

## 16. Segment Position

The `Segment Position` of an element refers to the position of the first octet of the `Element ID` of that element, measured in octets, from the beginning of the `Element Data` section of the containing `Segment` element. In other words, the `Segment Position` of an element is the distance in octets from the beginning of its containing `Segment` element minus the size of the `Element ID` and `Element Data Size` of that `Segment` element. The `Segment Position` of the first `Child Element` of the `Segment` element is 0. An element that is not stored within a `Segment` element, such as the elements of the `EBML Header`, do not have a `Segment Position`.¶

### 16.1. Segment Position Exception

Elements that are defined to store a `Segment Position` MAY define reserved values to indicate a special meaning.¶

### 16.2. Example of Segment Position

This table presents an example of `Segment Position` by showing a hexadecimal representation of a very small Matroska file with labels to show the offsets in octets. The file contains a `Segment` element with an `Element ID` of "0x18538067" and a `MuxingApp` element with an `Element ID` of "0x4D80".¶

         0                             1                             2
         0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  6  7  8  9  0
         +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
       0 |1A|45|DF|A3|8B|42|82|88|6D|61|74|72|6F|73|6B|61|
         ^ EBML Header
       0 |                                               |18|53|80|67|
                                                         ^ Segment ID
      20 |93|
         ^ Segment Data Size
      20 |  |15|49|A9|66|8E|4D|80|84|69|65|74|66|57|41|84|69|65|74|66|
            ^ Start of Segment data
      20 |                 |4D|80|84|69|65|74|66|57|41|84|69|65|74|66|
                           ^ MuxingApp start

¶

In the above example, the `Element ID` of the `Segment` element is stored at offset 16, the `Element Data Size` of the `Segment` element is stored at offset 20, and the `Element Data` of the `Segment` element is stored at offset 21.¶

The `MuxingApp` element is stored at offset 26. Since the `Segment Position` of an element is calculated by subtracting the position of the `Element Data` of the containing `Segment` element from the position of that element, the `Segment Position` of the `MuxingApp` element in the above example is "26 - 21" or "5".¶

## 17. Linked Segments

Matroska provides several methods to link two or more `Segment` elements together to create a `Linked Segment`. A `Linked Segment` is a set of multiple `Segments` linked together into a single presentation by using Hard Linking or Medium Linking.¶

All `Segments` within a `Linked Segment` MUST have a `SegmentUUID`.¶

All `Segments` within a `Linked Segment` SHOULD be stored within the same directory or be quickly accessible based on their `SegmentUUID` in order to have a seamless transition between segments.¶

All `Segments` within a `Linked Segment` MAY set a `SegmentFamily` with a common value to make it easier for a `Matroska Player` to know which `Segments` are meant to be played together.¶

The `SegmentFilename`, `PrevFilename`, and `NextFilename` elements MAY also give hints on the original filenames that were used when the `Segment` links were created, in case some `SegmentUUIDs` are damaged.¶

### 17.1. Hard Linking

Hard Linking, also called "splitting", is the process of creating a `Linked Segment` by linking multiple `Segment` elements using the `NextUUID` and `PrevUUID` elements.¶

All `Segments` within a `Hard Linked Segment` MUST use the same `Tracks` list and `TimestampScale`.¶

Within a `Linked Segment`, the timestamps of `Block` and `SimpleBlock` MUST consecutively follow the timestamps of `Block` and `SimpleBlock` from the previous `Segment` in linking order.¶

With Hard Linking, the chapters of any `Segment` within the `Linked Segment` MUST only reference the current `Segment`. The `NextUUID` and `PrevUUID` reference the respective `SegmentUUID` values of the next and previous `Segments`.¶

The first `Segment` of a `Linked Segment` MUST NOT have a `PrevUUID` element. The last `Segment` of a `Linked Segment` MUST NOT have a `NextUUID` element.¶

For each node of the chain of `Segments` of a `Linked Segment`, at least one `Segment` MUST reference the other `Segment` within the chain.¶

In a chain of `Segments` of a `Linked Segment`, the `NextUUID` always takes precedence over the `PrevUUID`. Thus, if SegmentA has a `NextUUID` to SegmentB and SegmentB has a `PrevUUID` to SegmentC, the link to use is `NextUUID` between SegmentA and SegmentB, and SegmentC is not part of the `Linked Segment`.¶

If SegmentB has a `PrevUUID` to SegmentA, but SegmentA has no `NextUUID`, then the `Matroska Player` MAY consider these two `Segments` linked as SegmentA followed by SegmentB.¶

As an example, three `Segments` can be Hard Linked as a `Linked Segment` through cross-referencing each other with `SegmentUUID`, `PrevUUID`, and `NextUUID` as shown in this table:¶

Table 40: Usual Hard Linking UIDs
file name | `SegmentUUID` | `PrevUUID` | `NextUUID`
--- | --- | --- | ---
`start.mkv` | 71000c23cd310998 53fbc94dd984a5dd | Invalid | a77b3598941cb803 eac0fcdafe44fac9
`middle.mkv` | a77b3598941cb803 eac0fcdafe44fac9 | 71000c23cd310998 53fbc94dd984a5dd | 6c92285fa6d3e827 b198d120ea3ac674
`end.mkv` | 6c92285fa6d3e827 b198d120ea3ac674 | a77b3598941cb803 eac0fcdafe44fac9 | Invalid

An example where only the `NextUUID` element is used:¶

Table 41: Hard Linking without PrevUUID
file name | `SegmentUUID` | `PrevUUID` | `NextUUID`
--- | --- | --- | ---
`start.mkv` | 71000c23cd310998 53fbc94dd984a5dd | Invalid | a77b3598941cb803 eac0fcdafe44fac9
`middle.mkv` | a77b3598941cb803 eac0fcdafe44fac9 | n/a | 6c92285fa6d3e827 b198d120ea3ac674
`end.mkv` | 6c92285fa6d3e827 b198d120ea3ac674 | n/a | Invalid

An example where only the `PrevUUID` element is used:¶

Table 42: Hard Linking without NextUUID
file name | `SegmentUUID` | `PrevUUID` | `NextUUID`
--- | --- | --- | ---
`start.mkv` | 71000c23cd310998 53fbc94dd984a5dd | Invalid | n/a
`middle.mkv` | a77b3598941cb803 eac0fcdafe44fac9 | 71000c23cd310998 53fbc94dd984a5dd | n/a
`end.mkv` | 6c92285fa6d3e827 b198d120ea3ac674 | a77b3598941cb803 eac0fcdafe44fac9 | Invalid

An example where only the `middle.mkv` is using the `PrevUUID` and `NextUUID` elements:¶

Table 43: Hard Linking with Mixed UID Links
file name | `SegmentUUID` | `PrevUUID` | `NextUUID`
--- | --- | --- | ---
`start.mkv` | 71000c23cd310998 53fbc94dd984a5dd | Invalid | n/a
`middle.mkv` | a77b3598941cb803 eac0fcdafe44fac9 | 71000c23cd310998 53fbc94dd984a5dd | 6c92285fa6d3e827 b198d120ea3ac674
`end.mkv` | 6c92285fa6d3e827 b198d120ea3ac674 | n/a | Invalid

### 17.2. Medium Linking

Medium Linking creates relationships between `Segments` using `Ordered Chapters` (Section 20.1.3) and the `ChapterSegmentUUID` element. A `Chapter Edition` with `Ordered Chapters` MAY contain `Chapters` elements that reference timestamp ranges from other `Segments`. The `Segment` referenced by the `Ordered Chapter` via the `ChapterSegmentUUID` element SHOULD be played as part of a `Linked Segment`.¶

The timestamps of `Segment` content referenced by `Ordered Chapters` MUST be adjusted according to the cumulative duration of the previous `Ordered Chapters`.¶

As an example, a file named `intro.mkv` could have a `SegmentUUID` of "0xb16a58609fc7e60653a60c984fc11ead". Another file called `program.mkv` could use a `Chapter Edition` that contains two `Ordered Chapters`. The first chapter references the `Segment` of `intro.mkv` with the use of a `ChapterSegmentUUID`, `ChapterSegmentEditionUID`, `ChapterTimeStart`, and an optional `ChapterTimeEnd` element. The second chapter references content within the `Segment` of `program.mkv`. A `Matroska Player` SHOULD recognize the `Linked Segment` created by the use of `ChapterSegmentUUID` in an enabled `Edition` and present the reference content of the two `Segments` as a single presentation.¶

The `ChapterSegmentUUID` represents the `Segment` that holds the content to play in place of the `Linked Chapter`. The `ChapterSegmentUUID` MUST NOT be the `SegmentUUID` of its own `Segment`.¶

There are two ways to use a chapter link:¶

- Linked-Duration linking¶

- Linked-Edition linking¶

#### 17.2.1. Linked-Duration

A `Matroska Player` MUST play the content of the `Linked Segment` from the `ChapterTimeStart` until the `ChapterTimeEnd` timestamp in place of the `Linked Chapter`.¶

`ChapterTimeStart` and `ChapterTimeEnd` represent timestamps in the `Linked Segment` matching the value of `ChapterSegmentUUID`. Their values MUST be in the range of the `Linked Segment` duration.¶

The `ChapterTimeEnd` value MUST be set when using Linked-Duration chapter linking. `ChapterSegmentEditionUID` MUST NOT be set.¶

#### 17.2.2. Linked-Edition

A `Matroska Player` MUST play the whole `Linked Edition` of the `Linked Segment` in place of the `Linked Chapter`.¶

`ChapterSegmentEditionUID` represents a valid `Edition` from the `Linked Segment` matching the value of `ChapterSegmentUUID`.¶

When using Linked-Edition chapter linking, `ChapterTimeEnd` is OPTIONAL.¶

## 18. Track Flags

### 18.1. Default Flag

The Default flag is a hint for a `Matroska Player` indicating that a given track SHOULD be eligible to be automatically selected as the default track for a given language. If no tracks in a given language have the Default flag set, then all tracks in that language are eligible for automatic selection. This can be used to indicate that a track provides "regular service" that is suitable for users with default settings, as opposed to specialized services, such as commentary, captions for users with hearing impairments, or descriptive audio.¶

The `Matroska Player` MAY override the Default flag for any reason, including user preferences to prefer tracks providing accessibility services.¶

### 18.2. Forced Flag

The Forced flag tells the `Matroska Player` that it SHOULD display this subtitle track, even if user preferences usually would not call for any subtitles to be displayed alongside the audio track that is currently selected. This can be used to indicate that a track contains translations of on-screen text or dialogue spoken in a different language than the track's primary language.¶

### 18.3. Hearing-Impaired Flag

The Hearing-Impaired flag tells the `Matroska Player` that it SHOULD prefer this track when selecting a default track for a user with a hearing impairment and that it MAY prefer to select a different track when selecting a default track for a user that is not hearing impaired.¶

### 18.4. Visual-Impaired Flag

The Visual-Impaired flag tells the `Matroska Player` that it SHOULD prefer this track when selecting a default track for a user with a visual impairment and that it MAY prefer to select a different track when selecting a default track for a user that is not visually impaired.¶

### 18.5. Descriptions Flag

The Descriptions flag tells the `Matroska Player` that this track is suitable to play via a text-to-speech system for a user with a visual impairment and that it SHOULD NOT automatically select this track when selecting a default track for a user that is not visually impaired.¶

### 18.6. Original Flag

The Original flag tells the `Matroska Player` that this track is in the original language and that it SHOULD prefer this track if configured to prefer original-language tracks of this track's type.¶

### 18.7. Commentary Flag

The Commentary flag tells the `Matroska Player` that this track contains commentary on the content.¶

### 18.8. Track Operation

`TrackOperation` allows for the combination of multiple tracks to make a virtual one. It uses two separate system to combine tracks. One to create a 3D "composition" (left/right/background planes) and one to simplify join two tracks together to make a single track.¶

A track created with `TrackOperation` is a proper track with a UID and all its flags. However, the codec ID is meaningless because each "sub" track needs to be decoded by its own decoder before the "operation" is applied. The `Cues` elements corresponding to such a virtual track SHOULD be the union of the `Cues` elements for each of the tracks it's composed of (when the `Cues` are defined per track).¶

In the case of `TrackJoinBlocks`, the `Block` elements (from `BlockGroup` and `SimpleBlock`) of all the tracks SHOULD be used as if they were defined for this new virtual `Track`. When two `Block` elements have overlapping start or end timestamps, it's up to the underlying system to either drop some of these frames or render them the way they overlap. This situation SHOULD be avoided when creating such tracks, as you can never be sure of the end result on different platforms.¶

### 18.9. Overlay Track

An overlay track SHOULD be rendered in the same channel as the track it's linked to. When content is found in such a track, it SHOULD be played on the rendering channel instead of the original track.¶

### 18.10. Multi-planar and 3D Videos

There are two different ways to compress 3D videos: have each eye track in a separate track and have one track have both eyes combined inside (which is more efficient compression-wise). Matroska supports both ways.¶

For the single-track variant, there is the `StereoMode` element, which defines how planes are assembled in the track (mono or left-right combined). Odd values of `StereoMode` means the left plane comes first for more convenient reading. The pixel count of the track (`PixelWidth`/`PixelHeight`) is the raw number of pixels (for example, 3840x1080 for full HD side by side), and the `DisplayWidth`/`DisplayHeight` in pixels is the number of pixels for one plane (1920x1080 for that full HD stream). Old stereo 3D movies were displayed using anaglyph (cyan and red colors separated). For compatibility with such movies, there is a value of the `StereoMode` that corresponds to anaglyph.¶

There is also a "packed" mode (values 13 and 14) that consists of packing two frames together in a `Block` that uses lacing. The first frame is the left eye and the other frame is the right eye (or vice versa). The frames SHOULD be decoded in that order and are possibly dependent on each other (P and B frames).¶

For separate tracks, Matroska needs to define exactly which track does what. `TrackOperation` with `TrackCombinePlanes` does that. For more details, see Section 18.8 on how `TrackOperation` works.¶

The 3D support is still in infancy and may evolve to support more features.¶

The `StereoMode` used to be part of Matroska v2, but it didn't meet the requirement for multiple tracks. There was also a bug in [libmatroska] prior to 0.9.0 that would save/read it as `0x53B9` instead of `0x53B8`; see `OldStereoMode` (Section 5.1.4.1.28.5). `Matroska Readers` MAY support these legacy files by checking Matroska v2 or `0x53B9`. The older values of `StereoMode` were 0 (mono), 1 (right eye), 2 (left eye), and 3 (both eyes); these are the only values that can be found in `OldStereoMode`. They are not compatible with the `StereoMode` values found in Matroska v3 and above.¶

## 19. Default Track Selection

This section provides some example sets of `Tracks` and hypothetical user settings, along with indications of which ones a similarly configured `Matroska Player` SHOULD automatically select for playback by default in such a situation. A player MAY provide additional settings with more detailed controls for more nuanced scenarios. These examples are provided as guidelines to illustrate the intended usages of the various supported `Track` flags and their expected behaviors.¶

`Track` names are shown in English for illustrative purposes; actual files may have titles in the language of each track or provide titles in multiple languages.¶

### 19.1. Audio Selection

Example track set:¶

Table 44: Audio Tracks for Default Selection
No. | Type | Lang | Layout | Original | Default | Other Flags | Name
--- | --- | --- | --- | --- | --- | --- | ---
1 | Video | und | N/A | N/A | N/A | None |
2 | Audio | eng | 5.1 | 1 | 1 | None |
3 | Audio | eng | 2.0 | 1 | 1 | None |
4 | Audio | eng | 2.0 | 1 | 0 | Visual-Impaired | Descriptive audio
5 | Audio | esp | 5.1 | 0 | 1 | None |
6 | Audio | esp | 2.0 | 0 | 0 | Visual-Impaired | Descriptive audio
7 | Audio | eng | 2.0 | 1 | 0 | Commentary | Director's Commentary
8 | Audio | eng | 2.0 | 1 | 0 | None | Karaoke

The table above shows a file with seven audio tracks -- five in English and two in Spanish.¶

The English tracks all have the Original flag, indicating that English is the original content language.¶

Generally, the player will first consider the track languages. If the player has an option to prefer original-language audio and the user has enabled it, then it should prefer one of the tracks with the Original flag. If the user has configured to specifically prefer audio tracks in English or Spanish, the player should select one of the tracks in the corresponding language. The player may also wish to prefer a track with the Original flag if no tracks matching any of the user's explicitly preferred languages are available.¶

Two of the tracks have the Visual-Impaired flag. If the player has been configured to prefer such tracks, it should select one; otherwise, it should avoid them if possible.¶

If selecting an English track, when other settings have left multiple possible options, it may be useful to exclude the tracks that lack the Default flag. Here, one provides descriptive service for individuals with visual impairments (which has its own flag and may be automatically selected by user configuration but is unsuitable for users with default-configured players), one is a commentary track (which has its own flag and the player may or may not have specialized handling for), and the last contains karaoke versions of the music that plays during the film (which is an unusual specialized audio service that Matroska has no built-in support for indicating, so it's indicated in the track name instead). By not setting the Default flag on these specialized tracks, the file's author hints that they should not be automatically selected by a default-configured player.¶

Having narrowed its choices down, the example player now may have to select between tracks 2 and 3. The only difference between these tracks is their channel layouts: 2 is 5.1 surround, while 3 is stereo. If the player is aware that the output device is a pair of headphones or stereo speakers, it may wish to prefer the stereo mix automatically. On the other hand, if it knows that the device is a surround system, it may wish to prefer the surround mix.¶

If the player finishes analyzing all of the available audio tracks and finds that more than one seem equally and maximally preferable, it SHOULD default to the first of the group.¶

### 19.2. Subtitle Selection

Example track set:¶

Table 45: Subtitle Tracks for Default Selection
No. | Type | Lang | Original | Default | Forced | Other Flags | Name
--- | --- | --- | --- | --- | --- | --- | ---
1 | Video | und | N/A | N/A | N/A | None |
2 | Audio | fra | 1 | 1 | N/A | None |
3 | Audio | por | 0 | 1 | N/A | None |
4 | Subtitles | fra | 1 | 1 | 0 | None |
5 | Subtitles | fra | 1 | 0 | 0 | Hearing-Impaired | Captions for users with hearing impairments
6 | Subtitles | por | 0 | 1 | 0 | None |
7 | Subtitles | por | 0 | 0 | 1 | None | Signs
8 | Subtitles | por | 0 | 0 | 0 | Hearing-Impaired | SDH

The table above shows two audio tracks and five subtitle tracks. As we can see, French is the original language.¶

We'll start by discussing the case where the user prefers French (or original-language) audio (or has explicitly selected the French audio track) and also prefers French subtitles.¶

In this case, if the player isn't configured to display captions when the audio matches their preferred subtitle languages, the player doesn't need to select a subtitle track at all.¶

If the user has indicated that they want captions to be displayed, the selection simply comes down to whether hearing-impaired subtitles are preferred.¶

The situation for a user who prefers Portuguese subtitles starts out somewhat analogous. If they select the original French audio (either by explicit audio language preference, preference for original-language tracks, or explicitly selecting that track), then the selection once again comes down to the hearing-impaired preference.¶

However, the case where the Portuguese audio track is selected has an important catch: a Forced track in Portuguese is present. This may contain translations of on-screen text from the video track or of portions of the audio that are not translated (music, for instance). This means that even if the user's preferences wouldn't normally call for captions here, the Forced track should be selected nonetheless, rather than selecting no track at all. On the other hand, if the user's preferences do call for captions, the non-Forced tracks should be preferred, as the Forced track will not contain captioning for the dialogue.¶

## 20. Chapters

The Matroska `Chapters` system can have multiple `Editions`, and each `Edition` can consist of `Simple Chapters` where a chapter start time is used as a marker in the timeline only. An `Edition` can be more complex with `Ordered Chapters` where a chapter end timestamp is additionally used or much more complex with `Linked Chapters`. The Matroska `Chapters` system can also have a menu structure borrowed from the DVD-menu system [DVD-Video] or have its own built-in Matroska menu structure.¶

### 20.1. EditionEntry

The `EditionEntry` is also called an `Edition`. An `Edition` contains a set of `Edition` flags and MUST contain at least one `ChapterAtom` element. `Chapters` are always inside an `Edition` (or a `Chapter` itself is part of an `Edition`). Multiple `Editions` are allowed. Some of these `Editions` MAY be ordered and others not.¶

#### 20.1.1. EditionFlagDefault

Only one `Edition` SHOULD have an `EditionFlagDefault` flag set to `true`.¶

#### 20.1.2. Default Edition

The `Default Edition` is the `Edition` that a `Matroska Player` SHOULD use for playback by default.¶

The first `Edition` with the `EditionFlagDefault` flag set to `true` is the `Default Edition`.¶

When all `EditionFlagDefault` flags are set to `false`, then the first `Edition` is the `Default Edition`.¶

Table 46: Default Edition, All Default
Edition | FlagDefault | Default Edition
--- | --- | ---
Edition 1 | true | X
Edition 2 | true |
Edition 3 | true |

Table 47: Default Edition, No Default
Edition | FlagDefault | Default Edition
--- | --- | ---
Edition 1 | false | X
Edition 2 | false |
Edition 3 | false |

Table 48: Default Edition, With Default
Edition | FlagDefault | Default Edition
--- | --- | ---
Edition 1 | false |
Edition 2 | true | X
Edition 3 | false |

#### 20.1.3. EditionFlagOrdered

The `EditionFlagOrdered` flag is a significant feature, as it enables an `Edition` of `Ordered Chapters` that defines and arranges a virtual timeline rather than simply labeling points within the timeline. For example, with `Editions` of `Ordered Chapters`, a single `Matroska file` can present multiple edits of a film without duplicating content. Alternatively, if a videotape is digitized in full, one `Ordered Edition` could present the full content (including colorbars, countdown, slate, a feature presentation, and black frames), while another `Edition` of `Ordered Chapters` can use `Chapters` that only mark the intended presentation with the colorbars and other ancillary visual information excluded. If an `Edition` of `Ordered Chapters` is enabled, then the `Matroska Player` MUST play those `Chapters` in their stored order from the timestamp marked in the `ChapterTimeStart` element to the timestamp marked in to `ChapterTimeEnd` element.¶

If the `EditionFlagOrdered` flag evaluates to "0", `Simple Chapters` are used and only the `ChapterTimeStart` of a `Chapter` is used as a chapter mark to jump to the predefined point in the timeline. With `Simple Chapters`, a `Matroska Player` MUST ignore certain elements inside a `Chapters` element. In that case, these elements are informational only.¶

The following list shows the different `Chapters` elements only found in `Ordered Chapters`.¶

- `ChapterAtom\ChapterSegmentUUID`¶

- `ChapterAtom\ChapterSegmentEditionUID`¶

- `ChapterAtom\ChapProcess`¶

- `Info\ChapterTranslate`¶

- `TrackEntry\TrackTranslate`¶

Furthermore, there are other EBML elements that could be used if the `EditionFlagOrdered` evaluates to "1".¶

##### 20.1.3.1. Ordered-Edition and Matroska Segment Linking

Hard Linking:

  `Ordered Chapters` supersede the `Hard Linking`.¶

Medium Linking:

  `Ordered Chapters` are used in a normal way and can be combined with the `ChapterSegmentUUID` element, which establishes a link to another `Segment`.¶

See Section 17 on `Linked Segment`s for more information about `Hard Linking` and `Medium Linking`.¶

### 20.2. ChapterAtom

The `ChapterAtom` is also called a `Chapter`.¶

#### 20.2.1. ChapterTimeStart

`ChapterTimeStart` is the timestamp of the start of `Chapter` with nanosecond accuracy and is not scaled by `TimestampScale`. For `Simple Chapters`, this is the position of the chapter markers in the timeline.¶

#### 20.2.2. ChapterTimeEnd

`ChapterTimeEnd` is the timestamp of the end of `Chapter` with nanosecond accuracy and is not scaled by `TimestampScale`. The timestamp defined by the `ChapterTimeEnd` is not part of the `Chapter`. A `Matroska Player` calculates the duration of this `Chapter` using the difference between the `ChapterTimeEnd` and `ChapterTimeStart`. The end timestamp MUST be greater than or equal to the start timestamp.¶

When the `ChapterTimeEnd` timestamp is equal to the `ChapterTimeStart` timestamp, the timestamp is included in the `Chapter`. It can be useful to put markers in a file or add chapter commands with ordered chapter commands without having to play anything; see Section 5.1.7.1.4.14.¶

Table 49: ChapterTimeEnd Usage Possibilities
Chapter | Start timestamp | End timestamp | Duration
--- | --- | --- | ---
Chapter 1 | 0 | 1000000000 | 1000000000
Chapter 2 | 1000000000 | 5000000000 | 4000000000
Chapter 3 | 6000000000 | 6000000000 | 0
Chapter 4 | 9000000000 | 8000000000 | Invalid (-1000000000)

#### 20.2.3. Nested Chapters

A `ChapterAtom` element can contain other `ChapterAtom` elements. That element is a `Parent Chapter`, and the `ChapterAtom` elements it contains are `Nested Chapters`.¶

`Nested Chapters` can be useful to tag small parts of a `Segment` that already have tags or add Chapter Codec commands on smaller parts of a `Segment` that already have Chapter Codec commands.¶

The `ChapterTimeStart` of a `Nested Chapter` MUST be greater than or equal to the `ChapterTimeStart` of its `Parent Chapter`.¶

If the `Parent Chapter` of a `Nested Chapter` has a `ChapterTimeEnd`, the `ChapterTimeStart` of that `Nested Chapter` MUST be smaller than or equal to the `ChapterTimeEnd` of the `Parent Chapter`.¶

#### 20.2.4. Nested Chapters in Ordered Chapters

The `ChapterTimeEnd` of the lowest level of `Nested Chapters` MUST be set for `Ordered Chapters`.¶

When used with `Ordered Chapters`, the `ChapterTimeEnd` value of a `Parent Chapter` is useless for playback, as the proper playback sections are described in its `Nested Chapters`. The `ChapterTimeEnd` SHOULD NOT be set in `Parent Chapters` and MUST be ignored for playback.¶

#### 20.2.5. ChapterFlagHidden

Each `Chapter`'s `ChapterFlagHidden` flag works independently of `Parent Chapters`. A `Nested Chapter` with a `ChapterFlagHidden` flag that evaluates to "0" remains visible in the user interface even if the `Parent Chapter`'s `ChapterFlagHidden` flag is set to "1".¶

Table 50: ChapterFlagHidden Nested Visibility
Chapter + Nested Chapter | ChapterFlagHidden | visible
--- | --- | ---
Chapter 1 | 0 | yes
Nested Chapter 1.1 | 0 | yes
Nested Chapter 1.2 | 1 | no
Chapter 2 | 1 | no
Nested Chapter 2.1 | 0 | yes
Nested Chapter 2.2 | 1 | no

### 20.4. Physical Types

Each level can have different meanings for audio and video. The `ORIGINAL_MEDIA_TYPE` tag [MatroskaTags] can be used to specify a string for ChapterPhysicalEquiv = 60. Here is the list of possible levels for both audio and video:¶

Table 51: ChapterPhysicalEquiv Meaning per Track Type
Value | Audio | Video | Comment
--- | --- | --- | ---
70 | SET / PACKAGE | SET / PACKAGE | the collection of different media
60 | CD / 12" / 10" / 7" / TAPE / MINIDISC / DAT | DVD / VHS / LASERDISC | the physical medium like a CD or a DVD
50 | SIDE | SIDE | when the original medium (LP/DVD) has different sides
40 | - | LAYER | another physical level on DVDs
30 | SESSION | SESSION | as found on CDs and DVDs
20 | TRACK | - | as found on audio CDs
10 | INDEX | - | the first logical level of the side/medium

### 20.5. Chapter Examples

#### 20.5.1. Example 1: Basic Chaptering

In this example, a movie is split in different chapters. It could also just be an audio file (album) in which each track corresponds to a chapter.¶

- 00000 ms - 05000 ms: Intro¶
- 05000 ms - 25000 ms: Before the crime¶
- 25000 ms - 27500 ms: The crime¶
- 27500 ms - 38000 ms: After the crime¶
- 38000 ms - 43000 ms: Credits¶

This translates to Matroska form, with the EBML tree shown as follows in XML:¶

    <Chapters>
      <EditionEntry>
        <EditionUID>16603393396715046047</EditionUID>
        <ChapterAtom>
          <ChapterUID>1193046</ChapterUID>
          <ChapterTimeStart>0</ChapterTimeStart>
          <ChapterTimeEnd>5000000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Intro</ChapString>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>2311527</ChapterUID>
          <ChapterTimeStart>5000000000</ChapterTimeStart>
          <ChapterTimeEnd>25000000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Before the crime</ChapString>
          </ChapterDisplay>
          <ChapterDisplay>
            <ChapString>Avant le crime</ChapString>
            <ChapLanguage>fra</ChapLanguage>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>3430008</ChapterUID>
          <ChapterTimeStart>25000000000</ChapterTimeStart>
          <ChapterTimeEnd>27500000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>The crime</ChapString>
          </ChapterDisplay>
          <ChapterDisplay>
            <ChapString>Le crime</ChapString>
            <ChapLanguage>fra</ChapLanguage>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>4548489</ChapterUID>
          <ChapterTimeStart>27500000000</ChapterTimeStart>
          <ChapterTimeEnd>38000000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>After the crime</ChapString>
          </ChapterDisplay>
          <ChapterDisplay>
            <ChapString>Apres le crime</ChapString>
            <ChapLanguage>fra</ChapLanguage>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>5666960</ChapterUID>
          <ChapterTimeStart>38000000000</ChapterTimeStart>
          <ChapterTimeEnd>43000000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Credits</ChapString>
          </ChapterDisplay>
          <ChapterDisplay>
            <ChapString>Generique</ChapString>
            <ChapLanguage>fra</ChapLanguage>
          </ChapterDisplay>
        </ChapterAtom>
      </EditionEntry>
    </Chapters>

Figure 25: Basic Chapters Example

#### 20.5.2. Example 2: Nested Chapters

In this example, an (existing) album is split into different chapters, and one of them contains another splitting.¶

##### 20.5.2.1. The Micronauts "Bleep To Bleep"

- 00:00 - 12:28: Baby wants to Bleep/Rock¶

  - 00:00 - 04:38: Baby wants to bleep (pt.1)¶
  - 04:38 - 07:12: Baby wants to rock¶
  - 07:12 - 10:33: Baby wants to bleep (pt.2)¶
  - 10:33 - 12:28: Baby wants to bleep (pt.3)¶
- 12:30 - 19:38: Bleeper_O+2¶
- 19:40 - 22:20: Baby wants to bleep (pt.4)¶
- 22:22 - 25:18: Bleep to bleep¶
- 25:20 - 33:35: Baby wants to bleep (k)¶
- 33:37 - 44:28: Bleeper¶

This translates to Matroska form, with the EBML tree shown as follows in XML:¶

    <Chapters>
      <EditionEntry>
        <EditionUID>1281690858003401414</EditionUID>
        <ChapterAtom>
          <ChapterUID>1</ChapterUID>
          <ChapterTimeStart>0</ChapterTimeStart>
          <ChapterTimeEnd>748000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Baby wants to Bleep/Rock</ChapString>
          </ChapterDisplay>
          <ChapterAtom>
            <ChapterUID>2</ChapterUID>
            <ChapterTimeStart>0</ChapterTimeStart>
            <ChapterTimeEnd>278000000</ChapterTimeEnd>
            <ChapterDisplay>
              <ChapString>Baby wants to bleep (pt.1)</ChapString>
            </ChapterDisplay>
          </ChapterAtom>
          <ChapterAtom>
            <ChapterUID>3</ChapterUID>
            <ChapterTimeStart>278000000</ChapterTimeStart>
            <ChapterTimeEnd>432000000</ChapterTimeEnd>
            <ChapterDisplay>
              <ChapString>Baby wants to rock</ChapString>
            </ChapterDisplay>
          </ChapterAtom>
          <ChapterAtom>
            <ChapterUID>4</ChapterUID>
            <ChapterTimeStart>432000000</ChapterTimeStart>
            <ChapterTimeEnd>633000000</ChapterTimeEnd>
            <ChapterDisplay>
              <ChapString>Baby wants to bleep (pt.2)</ChapString>
            </ChapterDisplay>
          </ChapterAtom>
          <ChapterAtom>
            <ChapterUID>5</ChapterUID>
            <ChapterTimeStart>633000000</ChapterTimeStart>
            <ChapterTimeEnd>748000000</ChapterTimeEnd>
            <ChapterDisplay>
              <ChapString>Baby wants to bleep (pt.3)</ChapString>
            </ChapterDisplay>
          </ChapterAtom>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>6</ChapterUID>
          <ChapterTimeStart>750000000</ChapterTimeStart>
          <ChapterTimeEnd>1178500000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Bleeper_O+2</ChapString>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>7</ChapterUID>
          <ChapterTimeStart>1180500000</ChapterTimeStart>
          <ChapterTimeEnd>1340000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Baby wants to bleep (pt.4)</ChapString>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>8</ChapterUID>
          <ChapterTimeStart>1342000000</ChapterTimeStart>
          <ChapterTimeEnd>1518000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Bleep to bleep</ChapString>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>9</ChapterUID>
          <ChapterTimeStart>1520000000</ChapterTimeStart>
          <ChapterTimeEnd>2015000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Baby wants to bleep (k)</ChapString>
          </ChapterDisplay>
        </ChapterAtom>
        <ChapterAtom>
          <ChapterUID>10</ChapterUID>
          <ChapterTimeStart>2017000000</ChapterTimeStart>
          <ChapterTimeEnd>2668000000</ChapterTimeEnd>
          <ChapterDisplay>
            <ChapString>Bleeper</ChapString>
          </ChapterDisplay>
        </ChapterAtom>
      </EditionEntry>
    </Chapters>

Figure 26: Nested Chapters Example

## 21. Attachments

Matroska supports storage of related files and data in the `Attachments` element (a `Top-Level Element`). `Attachments` elements can be used to store related cover art, font files, transcripts, reports, error recovery files, pictures, text-based annotations, copies of specifications, or other ancillary files related to the `Segment`.¶

`Matroska Readers` MUST NOT execute files stored as `Attachments` elements.¶

### 21.1. Cover Art

This section defines a set of guidelines for the storage of cover art in Matroska files. A `Matroska Reader` MAY use embedded cover art to display a representational still-image depiction of the multimedia contents of the Matroska file.¶

Only [JPEG] and PNG [RFC2083] image formats SHOULD be used for cover art pictures.¶

There can be two different covers for a movie/album: a portrait style (e.g., a DVD case) and a landscape style (e.g., a wide banner ad).¶

There can be two versions of the same cover: the `normal cover` and the `small cover`. The dimension of the `normal cover` SHOULD be 600 pixels on the smallest side (e.g., 960x600 for landscape, 600x800 for portrait, or 600x600 for square). The dimension of the `small cover` SHOULD be 120 pixels on the smallest side (e.g., 192x120 or 120x160).¶

Versions of cover art can be differentiated by the filename, which is stored in the `FileName` element. The default filename of the `normal cover` in square or portrait mode is `cover.(jpg|png)`. When stored, the `normal cover` SHOULD be the first `Attachments` element in storage order. The `small cover` SHOULD be prefixed with "small_", such as `small_cover.(jpg|png)`. The landscape variant SHOULD be suffixed with "_land", such as `cover_land.(jpg|png)`. The filenames are case-sensitive.¶

The following table provides examples of file names for cover art in `Attachments`.¶

Table 52: Cover Art Filenames
File Name | Image Orientation | Pixel Length of Smallest Side
--- | --- | ---
cover.jpg | Portrait or square | 600
small_cover.png | Portrait or square | 120
cover_land.png | Landscape | 600
small_cover_land.jpg | Landscape | 120

### 21.2. Font Files

Font files MAY be added to a Matroska file as Attachments so that the font file may be used to display an associated subtitle track. This allows the presentation of a Matroska file to be consistent in various environments where the needed fonts might not be available on the local system.¶

Depending on the font format in question, each font file can contain multiple font variants. Each font variant has a name that will be referred to as Font Name from now on. This Font Name can be different from the Attachment's `FileName`, even when disregarding the extension. In order to select a font for display, a `Matroska Player` SHOULD consider both the Font Name and the base name of the Attachment's `FileName`, preferring the former when there are multiple matches.¶

Subtitle codecs, such as SubStation Alpha (SSA) and Advanced SubStation Alpha (ASS), usually refer to a font by its Font Name, not by its filename. If none of the Attachments are a match for the Font Name, the `Matroska Player` SHOULD attempt to find a system font whose Font Name matches the one used in the subtitle track.¶

Since loading fonts temporarily can take a while, a `Matroska Player` usually loads or installs all the fonts found in attachments so they are ready to be used during playback. Failure to use the font attachment might result in incorrect rendering of the subtitles.¶

If a selected subtitle track has some `AttachmentLink` elements, the player MAY restrict its font rendering to use only these fonts.¶

A `Matroska Player` SHOULD handle the official font media types from [RFC8081] when the system can handle the type:¶

- font/sfnt: Generic SFNT Font Type¶

- font/ttf: TrueType Font (TTF) Font Type¶

- font/otf: OpenType Layout (OTF) Font Type¶

- font/collection: Collection Font Type¶

- font/woff: WOFF 1.0¶

- font/woff2: WOFF 2.0¶

Fonts in Matroska existed long before [RFC8081]. A few unofficial media types for fonts were used in existing files. Therefore, it is RECOMMENDED for a `Matroska Player` to support the following legacy media types for font attachments:¶

- application/x-truetype-font: TrueType fonts, equivalent to `font/ttf` and sometimes `font/otf`¶

- application/x-font-ttf: TrueType fonts, equivalent to `font/ttf`¶

- application/vnd.ms-opentype: OpenType Layout fonts, equivalent to `font/otf`¶

- application/font-sfnt: Generic SFNT Font Type, equivalent to `font/sfnt`¶

- application/font-woff: WOFF 1.0, equivalent to `font/woff`¶

There may also be some font attachments with the `application/octet-stream` media type. In that case, the `Matroska Player` MAY try to guess the font type by checking the file extension of the `AttachedFile\FileName` string. Common file extensions for fonts are:¶

- `.ttf` for TrueType fonts, equivalent to `font/ttf`¶

- `.otf` for OpenType Layout fonts, equivalent to `font/otf`¶

- `.ttc` for Collection fonts, equivalent to `font/collection`¶

The file extension check MUST be case-insensitive.¶

`Matroska Writers` SHOULD use a valid font media type from [RFC8081] in the `AttachedFile\FileMediaType` of the font attachment. They MAY use the media types found in older files when compatibility with older players is necessary.¶

## 22. Cues

The `Cues` element provides an index of certain `Cluster` elements to allow for optimized seeking to absolute timestamps within the `Segment`. The `Cues` element contains one or many `CuePoint` elements, each of which MUST reference an absolute timestamp (via the `CueTime` element), a `Track` (via the `CueTrack` element), and a `Segment Position` (via the `CueClusterPosition` element). Additional non-mandated elements are part of the `CuePoint` element, such as `CueDuration`, `CueRelativePosition`, `CueCodecState`, and others that provide any `Matroska Reader` with additional information to use in the optimization of seeking performance.¶

### 22.1. Recommendations

The following recommendations are provided to optimize Matroska performance.¶

- Unless Matroska is used as a live stream, it SHOULD contain a `Cues` element.¶

- For each video track, each keyframe SHOULD be referenced by a `CuePoint` element.¶

- It is RECOMMENDED to not reference non-keyframes of video tracks in `Cues` unless it references a `Cluster` element that contains a `CodecState` element but no keyframes.¶

- For each subtitle track present, each subtitle frame SHOULD be referenced by a `CuePoint` element with a `CueDuration` element.¶

- References to audio tracks MAY be skipped in `CuePoint` elements if a video track is present. When included, the `CuePoint` elements SHOULD reference audio keyframes once every 500 milliseconds at most.¶

- If the referenced frame is not stored within the first `SimpleBlock` or first `BlockGroup` within its `Cluster` element, then the `CueRelativePosition` element SHOULD be written to reference where in the `Cluster` the reference frame is stored.¶

- If a `CuePoint` element references a `Cluster` element that includes a `CodecState` element, then that `CuePoint` element MUST use a `CueCodecState` element.¶

- `CuePoint` elements SHOULD be numerically sorted in storage order by the value of the `CueTime` element.¶

## 23. Matroska Streaming

In Matroska, there are two kinds of streaming: file access and livestreaming.¶

### 23.1. File Access

File access can simply be reading a file located on your computer, but it also includes accessing a file from an HTTP (web) server or Common Internet File System (CIFS) (Windows share) server. These protocols are usually safe from reading errors, and seeking in the stream is possible. However, when a file is stored far away or on a slow server, seeking can be an expensive operation and should be avoided. When followed, the guidelines in Section 25 help reduce the number of seeking operations for regular playback and also have the playback start quickly without needing to read lot of data first (like a `Cues` element, `Attachments` element, or `SeekHead` element).¶

Matroska, having a small overhead, is well suited for storing music/videos on file servers without a big impact on the bandwidth used. Matroska does not require the index to be loaded before playing, which allows playback to start very quickly. The index can be loaded only when seeking is requested the first time.¶

### 23.2. Livestreaming

Livestreaming is the equivalent of television broadcasting on the Internet. There are two families of servers for livestreaming: RTP / Real-Time Streaming Protocol (RTSP) and HTTP. Matroska is not meant to be used over RTP. RTP already has timing and channel mechanisms that would be wasted if doubled in Matroska. Additionally, having the same information at the RTP and Matroska level would be a source of confusion if they do not match. Livestreaming of Matroska over file-like protocols like HTTP, QUIC, etc., is possible.¶

A live Matroska stream is different from a file because it usually has no known end (only ending when the client disconnects). For this, all bits of the "size" portion of the `Segment` element MUST be set to 1. Another option is to concatenate `Segment` elements with known sizes, one after the other. This solution allows a change of codec/resolution between each segment. For example, this allows for a switch between 4:3 and 16:9 in a television program.¶

When `Segment` elements are continuous, certain elements (like `SeekHead`, `Cues`, `Chapters`, and `Attachments`) MUST NOT be used.¶

It is possible for a `Matroska Player` to detect that a stream is not seekable. If the stream has neither a `SeekHead` list nor a `Cues` list at the beginning of the stream, it SHOULD be considered non-seekable. Even though it is possible to seek forward in the stream, it is NOT RECOMMENDED.¶

In the context of live radio or web TV, it is possible to "tag" the content while it is playing. The `Tags` element can be placed between `Clusters` each time it is necessary. In that case, the new `Tags` element MUST reset the previously encountered `Tags` elements and use the new values instead.¶

## 24. Tags

### 24.1. Tags Precedence

Tags allow tagging all kinds of Matroska parts with very detailed metadata in multiple languages.¶

Some Matroska elements also contain their own string value, like the track `Name` element (Section 5.1.4.1.18) or the `ChapString` element (Section 5.1.7.1.4.10).¶

The following Matroska elements can also be defined with tags:¶

- The track `Name` element (Section 5.1.4.1.18) corresponds to a tag with the `TagTrackUID` (Section 5.1.8.1.1.3) set to the given track, a `TagName` of `TITLE` (Section 5.1.8.1.2.1), and a `TagLanguage` (Section 5.1.8.1.2.2) or `TagLanguageBCP47` (Section 5.1.8.1.2.3) of "und".¶

- The `ChapString` element (Section 5.1.7.1.4.10) corresponds to a tag with the `TagChapterUID` (Section 5.1.8.1.1.5) set to the same chapter UID, a `TagName` of `TITLE` (Section 5.1.8.1.2.1), and a `TagLanguage` (Section 5.1.8.1.2.2) or `TagLanguageBCP47` (Section 5.1.8.1.2.3) matching the `ChapLanguage` (Section 5.1.7.1.4.11) or `ChapLanguageBCP47` (Section 5.1.7.1.4.12), respectively.¶

- The `FileDescription` element (Section 5.1.6.1.1) of an attachment corresponds to a tag with the `TagAttachmentUID` (Section 5.1.8.1.1.6) set to the given attachment, a `TagName` of `TITLE` (Section 5.1.8.1.2.1), and a `TagLanguage` (Section 5.1.8.1.2.2) or `TagLanguageBCP47` (Section 5.1.8.1.2.3) of "und".¶

When both values exist in the file, the value found in Tags takes precedence over the value found in the original location of the element. For example, if you have a `TrackEntry\Name` element and a tag value `TITLE` for that track in a Matroska `Segment`, the tag value string SHOULD be used instead of the `TrackEntry\Name` string to identify the track.¶

As the Tag element is optional, a lot of `Matroska Readers` do not handle it and will not use the tags value when it's found. Thus, for maximum compatibility, it's usually better to put the strings in the `TrackEntry`, `ChapterAtom`, and `Attachments` elements and keep the tags matching these values if tags are also used.¶

### 24.2. Tag Levels

Tag elements allow tagging information on multiple levels, with each level having a `TargetTypeValue` (Section 5.1.8.1.1.1). An element for a given `TargetTypeValue` also applies to the lower levels denoted by smaller `TargetTypeValue` values. If an upper value doesn't apply to a level but the actual value to use is not known, an empty `TagString` (Section 5.1.8.1.2.5) or an empty `TagBinary` (Section 5.1.8.1.2.6) MUST be used as the tag value for this level.¶

See [MatroskaTags] for more details on common tag names, types, and descriptions.¶

## 25. Implementation Recommendations

### 25.1. Cluster

It is RECOMMENDED that each individual `Cluster` element contain no more than five seconds or five megabytes of content.¶

### 25.2. SeekHead

It is RECOMMENDED that the first `SeekHead` element be followed by a `Void` element to allow for the `SeekHead` element to be expanded to cover new `Top-Level Elements` that could be added to the Matroska file, such as `Tags`, `Chapters`, and `Attachments` elements.¶

The size of this `Void` element should be adjusted depending on the `Tags`, `Chapters`, and `Attachments` elements in the Matroska file.¶

### 25.3. Optimum Layouts

While there can be `Top-Level Elements` in any order, some orderings of elements are better than others. The following subsections detail optimum layouts for different use cases.¶

#### 25.3.1. Optimum Layout for a Muxer

This is the basic layout muxers should be using for an efficient playback experience:¶

- `SeekHead`¶
- `Info`¶
- `Tracks`¶
- `Chapters`¶
- `Attachments`¶
- `Tags`¶
- `Clusters`¶
- `Cues`¶

#### 25.3.2. Optimum Layout after Editing Tags

When tags from the previous layout need to be extended, they are moved to the end with the extra information. The location where the old tags were located is voided.¶

- `SeekHead`¶
- `Info`¶
- `Tracks`¶
- `Chapters`¶
- `Attachments`¶
- `Void`¶
- `Clusters`¶
- `Cues`¶
- `Tags`¶

#### 25.3.3. Optimum Layout with Cues at the Front

`Cues` are usually a big chunk of data referencing a lot of locations in the file. Players that want to seek in the file need to seek to the end of the file to access these locations. It is often better if they are placed early in the file. On the other hand, that means players that don't intend to seek will have to read/skip these data no matter what.¶

Because the `Cues` reference locations further in the file, it's often complicated to allocate the proper space for that element before all the locations are known. Therefore, this layout is rarely used:¶

- `SeekHead`¶
- `Info`¶
- `Tracks`¶
- `Chapters`¶
- `Attachments`¶
- `Tags`¶
- `Cues`¶
- `Clusters`¶

#### 25.3.4. Optimum Layout for Livestreaming

In livestreaming (Section 23.2), only a few elements make sense. For example, `SeekHead` and `Cues` are useless. All elements other than the `Clusters` MUST be placed before the `Clusters`.¶

- `Info`¶
- `Tracks`¶
- `Attachments` (rare)¶
- `Tags`¶
- `Clusters`¶

## 26. Security Considerations

Matroska inherits security considerations from EBML [RFC8794].¶

Attacks on a `Matroska Reader` could include:¶

- Storage of an arbitrary and potentially executable data within an `Attachments` element. `Matroska Readers` that extract or use data from `Matroska Attachments` SHOULD check that the data adheres to expectations or not use the attachment.¶

- A `Matroska Attachment` with an inaccurate media type.¶

- Damage to the Encryption and Compression fields (Section 14) that would result in bogus binary data interpreted by the decoder.¶

- Chapter Codecs running unwanted commands on the host system.¶

The same error handling done for EBML applies to Matroska files. Particular error handling is not covered in this specification, as this is depends on the goal of the `Matroska Readers`. `Matroska Readers` decide how to handle the errors whether or not they are recoverable in their code. For example, if the checksum of the `\Segment\Tracks` is invalid, some could decide to try to read the data anyway, some will just reject the file, and most will not even check it.¶

`Matroska Reader` implementations need to be robust against malicious payloads. Those related to denial of service are outlined in Section 2.1 of [RFC4732].¶

Although rarer, the same may apply to a `Matroska Writer`. Malicious stream data must not cause the `Matroska Writer` to misbehave, as this might allow an attacker access to transcoding gateways.¶

As an audio/video container format, a Matroska file or stream will potentially encapsulate numerous byte streams created with a variety of codecs. Implementers will need to consider the security considerations of these encapsulated formats.¶

## 27. IANA Considerations

### 27.1. Matroska Element IDs Registry

IANA has created a new registry called the "Matroska Element IDs" registry.¶

To register a new Element ID in this registry, one needs an Element ID, an Element Name, a Change Controller, and an optional Reference to a document describing the Element ID.¶

Element IDs are encoded using the VINT mechanism described in Section 4 of [RFC8794] and can be between one and five octets long. Five-octet Element IDs are possible only if declared in the EBML Header.¶

Element IDs are described in Section 5 of [RFC8794], with the changes in [Err7189] and [Err7191].¶

One-octet Matroska Element IDs (range 0x80-0xFE) are to be allocated according to the "RFC Required" policy [RFC8126].¶

Two-octet Matroska Element IDs (range 0x407F-0x7FFE) are to be allocated according to the "Specification Required" policy [RFC8126].¶

Two-octet Matroska Element IDs between 0x0100 and 0x407E are not valid for use as an Element ID.¶

Three-octet (range 0x203FFF-0x3FFFFE) and four-octet Matroska Element IDs (range 0x101FFFFF-0x1FFFFFFE) are to be allocated according to the "First Come First Served" policy [RFC8126].¶

Three-octet Matroska Element IDs between 0x010000 and 0x203FFE are not valid for use as an Element ID.¶

Four-octet Matroska Element IDs between 0x01000000 and 0x101FFFFE are not valid for use as an Element ID.¶

The allowed values in the "Matroska Element IDs" registry are similar to the ones found in the "EBML Element IDs" registry defined in Section 17.1 of [RFC8794].¶

EBML Element IDs defined for the EBML Header -- as defined in Section 17.1 of [RFC8794] -- MUST NOT be used as Matroska Element IDs.¶

Given the scarcity of one-octet Element IDs, they should only be created to save space for elements found many times in a file (for example, `BlockGroup` or `Chapters`). The four-octet Element IDs are mostly for synchronization of large elements. They should only be used for such high-level elements. Elements that are not expected to be used often should use three-octet Element IDs.¶

Elements found in Appendix A have an assigned Matroska Element ID for historical reasons. These elements are not in use and SHOULD NOT be reused unless there are no other IDs available with the desired size. Such IDs are marked as "Reclaimed" in the "Matroska Element IDs" registry, as they could be used for other things in the future.¶

Table 53 shows the initial contents of the "Matroska Element IDs" registry. The Change Controller for the initial entries is the IETF.¶

Table 53: Initial Contents of "Matroska Element IDs" Registry
Element ID | Element Name | Reference
--- | --- | ---
0x80 | ChapterDisplay | RFC 9559, Section 5.1.7.1.4.9
0x83 | TrackType | RFC 9559, Section 5.1.4.1.3
0x85 | ChapString | RFC 9559, Section 5.1.7.1.4.10
0x86 | CodecID | RFC 9559, Section 5.1.4.1.21
0x88 | FlagDefault | RFC 9559, Section 5.1.4.1.5
0x8E | Slices | Reclaimed (RFC 9559, Appendix A.5)
0x91 | ChapterTimeStart | RFC 9559, Section 5.1.7.1.4.3
0x92 | ChapterTimeEnd | RFC 9559, Section 5.1.7.1.4.4
0x96 | CueRefTime | RFC 9559, Section 5.1.5.1.2.8
0x97 | CueRefCluster | Reclaimed (RFC 9559, Appendix A.37)
0x98 | ChapterFlagHidden | RFC 9559, Section 5.1.7.1.4.5
0x9A | FlagInterlaced | RFC 9559, Section 5.1.4.1.28.1
0x9B | BlockDuration | RFC 9559, Section 5.1.3.5.3
0x9C | FlagLacing | RFC 9559, Section 5.1.4.1.12
0x9D | FieldOrder | RFC 9559, Section 5.1.4.1.28.2
0x9F | Channels | RFC 9559, Section 5.1.4.1.29.3
0xA0 | BlockGroup | RFC 9559, Section 5.1.3.5
0xA1 | Block | RFC 9559, Section 5.1.3.5.1
0xA2 | BlockVirtual | Reclaimed (RFC 9559, Appendix A.3)
0xA3 | SimpleBlock | RFC 9559, Section 5.1.3.4
0xA4 | CodecState | RFC 9559, Section 5.1.3.5.6
0xA5 | BlockAdditional | RFC 9559, Section 5.1.3.5.2.2
0xA6 | BlockMore | RFC 9559, Section 5.1.3.5.2.1
0xA7 | Position | RFC 9559, Section 5.1.3.2
0xAA | CodecDecodeAll | Reclaimed (RFC 9559, Appendix A.22)
0xAB | PrevSize | RFC 9559, Section 5.1.3.3
0xAE | TrackEntry | RFC 9559, Section 5.1.4.1
0xAF | EncryptedBlock | Reclaimed (RFC 9559, Appendix A.15)
0xB0 | PixelWidth | RFC 9559, Section 5.1.4.1.28.6
0xB2 | CueDuration | RFC 9559, Section 5.1.5.1.2.4
0xB3 | CueTime | RFC 9559, Section 5.1.5.1.1
0xB5 | SamplingFrequency | RFC 9559, Section 5.1.4.1.29.1
0xB6 | ChapterAtom | RFC 9559, Section 5.1.7.1.4
0xB7 | CueTrackPositions | RFC 9559, Section 5.1.5.1.2
0xB9 | FlagEnabled | RFC 9559, Section 5.1.4.1.4
0xBA | PixelHeight | RFC 9559, Section 5.1.4.1.28.7
0xBB | CuePoint | RFC 9559, Section 5.1.5.1
0xC0 | TrickTrackUID | Reclaimed (RFC 9559, Appendix A.28)
0xC1 | TrickTrackSegmentUID | Reclaimed (RFC 9559, Appendix A.29)
0xC4 | TrickMasterTrackSegmentUID | Reclaimed (RFC 9559, Appendix A.32)
0xC6 | TrickTrackFlag | Reclaimed (RFC 9559, Appendix A.30)
0xC7 | TrickMasterTrackUID | Reclaimed (RFC 9559, Appendix A.31)
0xC8 | ReferenceFrame | Reclaimed (RFC 9559, Appendix A.12)
0xC9 | ReferenceOffset | Reclaimed (RFC 9559, Appendix A.13)
0xCA | ReferenceTimestamp | Reclaimed (RFC 9559, Appendix A.14)
0xCB | BlockAdditionID | Reclaimed (RFC 9559, Appendix A.9)
0xCC | LaceNumber | Reclaimed (RFC 9559, Appendix A.7)
0xCD | FrameNumber | Reclaimed (RFC 9559, Appendix A.8)
0xCE | Delay | Reclaimed (RFC 9559, Appendix A.10)
0xCF | SliceDuration | Reclaimed (RFC 9559, Appendix A.11)
0xD7 | TrackNumber | RFC 9559, Section 5.1.4.1.1
0xDB | CueReference | RFC 9559, Section 5.1.5.1.2.7
0xE0 | Video | RFC 9559, Section 5.1.4.1.28
0xE1 | Audio | RFC 9559, Section 5.1.4.1.29
0xE2 | TrackOperation | RFC 9559, Section 5.1.4.1.30
0xE3 | TrackCombinePlanes | RFC 9559, Section 5.1.4.1.30.1
0xE4 | TrackPlane | RFC 9559, Section 5.1.4.1.30.2
0xE5 | TrackPlaneUID | RFC 9559, Section 5.1.4.1.30.3
0xE6 | TrackPlaneType | RFC 9559, Section 5.1.4.1.30.4
0xE7 | Timestamp | RFC 9559, Section 5.1.3.1
0xE8 | TimeSlice | Reclaimed (RFC 9559, Appendix A.6)
0xE9 | TrackJoinBlocks | RFC 9559, Section 5.1.4.1.30.5
0xEA | CueCodecState | RFC 9559, Section 5.1.5.1.2.6
0xEB | CueRefCodecState | Reclaimed (RFC 9559, Appendix A.39)
0xED | TrackJoinUID | RFC 9559, Section 5.1.4.1.30.6
0xEE | BlockAddID | RFC 9559, Section 5.1.3.5.2.3
0xF0 | CueRelativePosition | RFC 9559, Section 5.1.5.1.2.3
0xF1 | CueClusterPosition | RFC 9559, Section 5.1.5.1.2.2
0xF7 | CueTrack | RFC 9559, Section 5.1.5.1.2.1
0xFA | ReferencePriority | RFC 9559, Section 5.1.3.5.4
0xFB | ReferenceBlock | RFC 9559, Section 5.1.3.5.5
0xFD | ReferenceVirtual | Reclaimed (RFC 9559, Appendix A.4)
0xFF | Reserved | RFC 9559
0x0100-0x407E | Not valid for use as an Element ID | RFC 9559, Section 27.1
0x41A4 | BlockAddIDName | RFC 9559, Section 5.1.4.1.17.2
0x41E4 | BlockAdditionMapping | RFC 9559, Section 5.1.4.1.17
0x41E7 | BlockAddIDType | RFC 9559, Section 5.1.4.1.17.3
0x41ED | BlockAddIDExtraData | RFC 9559, Section 5.1.4.1.17.4
0x41F0 | BlockAddIDValue | RFC 9559, Section 5.1.4.1.17.1
0x4254 | ContentCompAlgo | RFC 9559, Section 5.1.4.1.31.6
0x4255 | ContentCompSettings | RFC 9559, Section 5.1.4.1.31.7
0x437C | ChapLanguage | RFC 9559, Section 5.1.7.1.4.11
0x437D | ChapLanguageBCP47 | RFC 9559, Section 5.1.7.1.4.12
0x437E | ChapCountry | RFC 9559, Section 5.1.7.1.4.13
0x4444 | SegmentFamily | RFC 9559, Section 5.1.2.7
0x4461 | DateUTC | RFC 9559, Section 5.1.2.11
0x447A | TagLanguage | RFC 9559, Section 5.1.8.1.2.2
0x447B | TagLanguageBCP47 | RFC 9559, Section 5.1.8.1.2.3
0x4484 | TagDefault | RFC 9559, Section 5.1.8.1.2.4
0x4485 | TagBinary | RFC 9559, Section 5.1.8.1.2.6
0x4487 | TagString | RFC 9559, Section 5.1.8.1.2.5
0x4489 | Duration | RFC 9559, Section 5.1.2.10
0x44B4 | TagDefaultBogus | Reclaimed (RFC 9559, Appendix A.43)
0x450D | ChapProcessPrivate | RFC 9559, Section 5.1.7.1.4.16
0x45A3 | TagName | RFC 9559, Section 5.1.8.1.2.1
0x45B9 | EditionEntry | RFC 9559, Section 5.1.7.1
0x45BC | EditionUID | RFC 9559, Section 5.1.7.1.1
0x45DB | EditionFlagDefault | RFC 9559, Section 5.1.7.1.2
0x45DD | EditionFlagOrdered | RFC 9559, Section 5.1.7.1.3
0x465C | FileData | RFC 9559, Section 5.1.6.1.4
0x4660 | FileMediaType | RFC 9559, Section 5.1.6.1.3
0x4661 | FileUsedStartTime | Reclaimed (RFC 9559, Appendix A.41)
0x4662 | FileUsedEndTime | Reclaimed (RFC 9559, Appendix A.42)
0x466E | FileName | RFC 9559, Section 5.1.6.1.2
0x4675 | FileReferral | Reclaimed (RFC 9559, Appendix A.40)
0x467E | FileDescription | RFC 9559, Section 5.1.6.1.1
0x46AE | FileUID | RFC 9559, Section 5.1.6.1.5
0x47E1 | ContentEncAlgo | RFC 9559, Section 5.1.4.1.31.9
0x47E2 | ContentEncKeyID | RFC 9559, Section 5.1.4.1.31.10
0x47E3 | ContentSignature | Reclaimed (RFC 9559, Appendix A.33)
0x47E4 | ContentSigKeyID | Reclaimed (RFC 9559, Appendix A.34)
0x47E5 | ContentSigAlgo | Reclaimed (RFC 9559, Appendix A.35)
0x47E6 | ContentSigHashAlgo | Reclaimed (RFC 9559, Appendix A.36)
0x47E7 | ContentEncAESSettings | RFC 9559, Section 5.1.4.1.31.11
0x47E8 | AESSettingsCipherMode | RFC 9559, Section 5.1.4.1.31.12
0x4D80 | MuxingApp | RFC 9559, Section 5.1.2.13
0x4DBB | Seek | RFC 9559, Section 5.1.1.1
0x5031 | ContentEncodingOrder | RFC 9559, Section 5.1.4.1.31.2
0x5032 | ContentEncodingScope | RFC 9559, Section 5.1.4.1.31.3
0x5033 | ContentEncodingType | RFC 9559, Section 5.1.4.1.31.4
0x5034 | ContentCompression | RFC 9559, Section 5.1.4.1.31.5
0x5035 | ContentEncryption | RFC 9559, Section 5.1.4.1.31.8
0x535F | CueRefNumber | Reclaimed (RFC 9559, Appendix A.38)
0x536E | Name | RFC 9559, Section 5.1.4.1.18
0x5378 | CueBlockNumber | RFC 9559, Section 5.1.5.1.2.5
0x537F | TrackOffset | Reclaimed (RFC 9559, Appendix A.18)
0x53AB | SeekID | RFC 9559, Section 5.1.1.1.1
0x53AC | SeekPosition | RFC 9559, Section 5.1.1.1.2
0x53B8 | StereoMode | RFC 9559, Section 5.1.4.1.28.3
0x53B9 | OldStereoMode | RFC 9559, Section 5.1.4.1.28.5
0x53C0 | AlphaMode | RFC 9559, Section 5.1.4.1.28.4
0x54AA | PixelCropBottom | RFC 9559, Section 5.1.4.1.28.8
0x54B0 | DisplayWidth | RFC 9559, Section 5.1.4.1.28.12
0x54B2 | DisplayUnit | RFC 9559, Section 5.1.4.1.28.14
0x54B3 | AspectRatioType | Reclaimed (RFC 9559, Appendix A.24)
0x54BA | DisplayHeight | RFC 9559, Section 5.1.4.1.28.13
0x54BB | PixelCropTop | RFC 9559, Section 5.1.4.1.28.9
0x54CC | PixelCropLeft | RFC 9559, Section 5.1.4.1.28.10
0x54DD | PixelCropRight | RFC 9559, Section 5.1.4.1.28.11
0x55AA | FlagForced | RFC 9559, Section 5.1.4.1.6
0x55AB | FlagHearingImpaired | RFC 9559, Section 5.1.4.1.7
0x55AC | FlagVisualImpaired | RFC 9559, Section 5.1.4.1.8
0x55AD | FlagTextDescriptions | RFC 9559, Section 5.1.4.1.9
0x55AE | FlagOriginal | RFC 9559, Section 5.1.4.1.10
0x55AF | FlagCommentary | RFC 9559, Section 5.1.4.1.11
0x55B0 | Colour | RFC 9559, Section 5.1.4.1.28.16
0x55B1 | MatrixCoefficients | RFC 9559, Section 5.1.4.1.28.17
0x55B2 | BitsPerChannel | RFC 9559, Section 5.1.4.1.28.18
0x55B3 | ChromaSubsamplingHorz | RFC 9559, Section 5.1.4.1.28.19
0x55B4 | ChromaSubsamplingVert | RFC 9559, Section 5.1.4.1.28.20
0x55B5 | CbSubsamplingHorz | RFC 9559, Section 5.1.4.1.28.21
0x55B6 | CbSubsamplingVert | RFC 9559, Section 5.1.4.1.28.22
0x55B7 | ChromaSitingHorz | RFC 9559, Section 5.1.4.1.28.23
0x55B8 | ChromaSitingVert | RFC 9559, Section 5.1.4.1.28.24
0x55B9 | Range | RFC 9559, Section 5.1.4.1.28.25
0x55BA | TransferCharacteristics | RFC 9559, Section 5.1.4.1.28.26
0x55BB | Primaries | RFC 9559, Section 5.1.4.1.28.27
0x55BC | MaxCLL | RFC 9559, Section 5.1.4.1.28.28
0x55BD | MaxFALL | RFC 9559, Section 5.1.4.1.28.29
0x55D0 | MasteringMetadata | RFC 9559, Section 5.1.4.1.28.30
0x55D1 | PrimaryRChromaticityX | RFC 9559, Section 5.1.4.1.28.31
0x55D2 | PrimaryRChromaticityY | RFC 9559, Section 5.1.4.1.28.32
0x55D3 | PrimaryGChromaticityX | RFC 9559, Section 5.1.4.1.28.33
0x55D4 | PrimaryGChromaticityY | RFC 9559, Section 5.1.4.1.28.34
0x55D5 | PrimaryBChromaticityX | RFC 9559, Section 5.1.4.1.28.35
0x55D6 | PrimaryBChromaticityY | RFC 9559, Section 5.1.4.1.28.36
0x55D7 | WhitePointChromaticityX | RFC 9559, Section 5.1.4.1.28.37
0x55D8 | WhitePointChromaticityY | RFC 9559, Section 5.1.4.1.28.38
0x55D9 | LuminanceMax | RFC 9559, Section 5.1.4.1.28.39
0x55DA | LuminanceMin | RFC 9559, Section 5.1.4.1.28.40
0x55EE | MaxBlockAdditionID | RFC 9559, Section 5.1.4.1.16
0x5654 | ChapterStringUID | RFC 9559, Section 5.1.7.1.4.2
0x56AA | CodecDelay | RFC 9559, Section 5.1.4.1.25
0x56BB | SeekPreRoll | RFC 9559, Section 5.1.4.1.26
0x5741 | WritingApp | RFC 9559, Section 5.1.2.14
0x5854 | SilentTracks | Reclaimed (RFC 9559, Appendix A.1)
0x58D7 | SilentTrackNumber | Reclaimed (RFC 9559, Appendix A.2)
0x61A7 | AttachedFile | RFC 9559, Section 5.1.6.1
0x6240 | ContentEncoding | RFC 9559, Section 5.1.4.1.31.1
0x6264 | BitDepth | RFC 9559, Section 5.1.4.1.29.4
0x63A2 | CodecPrivate | RFC 9559, Section 5.1.4.1.22
0x63C0 | Targets | RFC 9559, Section 5.1.8.1.1
0x63C3 | ChapterPhysicalEquiv | RFC 9559, Section 5.1.7.1.4.8
0x63C4 | TagChapterUID | RFC 9559, Section 5.1.8.1.1.5
0x63C5 | TagTrackUID | RFC 9559, Section 5.1.8.1.1.3
0x63C6 | TagAttachmentUID | RFC 9559, Section 5.1.8.1.1.6
0x63C9 | TagEditionUID | RFC 9559, Section 5.1.8.1.1.4
0x63CA | TargetType | RFC 9559, Section 5.1.8.1.1.2
0x6624 | TrackTranslate | RFC 9559, Section 5.1.4.1.27
0x66A5 | TrackTranslateTrackID | RFC 9559, Section 5.1.4.1.27.1
0x66BF | TrackTranslateCodec | RFC 9559, Section 5.1.4.1.27.2
0x66FC | TrackTranslateEditionUID | RFC 9559, Section 5.1.4.1.27.3
0x67C8 | SimpleTag | RFC 9559, Section 5.1.8.1.2
0x68CA | TargetTypeValue | RFC 9559, Section 5.1.8.1.1.1
0x6911 | ChapProcessCommand | RFC 9559, Section 5.1.7.1.4.17
0x6922 | ChapProcessTime | RFC 9559, Section 5.1.7.1.4.18
0x6924 | ChapterTranslate | RFC 9559, Section 5.1.2.8
0x6933 | ChapProcessData | RFC 9559, Section 5.1.7.1.4.19
0x6944 | ChapProcess | RFC 9559, Section 5.1.7.1.4.14
0x6955 | ChapProcessCodecID | RFC 9559, Section 5.1.7.1.4.15
0x69A5 | ChapterTranslateID | RFC 9559, Section 5.1.2.8.1
0x69BF | ChapterTranslateCodec | RFC 9559, Section 5.1.2.8.2
0x69FC | ChapterTranslateEditionUID | RFC 9559, Section 5.1.2.8.3
0x6D80 | ContentEncodings | RFC 9559, Section 5.1.4.1.31
0x6DE7 | MinCache | Reclaimed (RFC 9559, Appendix A.16)
0x6DF8 | MaxCache | Reclaimed (RFC 9559, Appendix A.17)
0x6E67 | ChapterSegmentUUID | RFC 9559, Section 5.1.7.1.4.6
0x6EBC | ChapterSegmentEditionUID | RFC 9559, Section 5.1.7.1.4.7
0x6FAB | TrackOverlay | Reclaimed (RFC 9559, Appendix A.23)
0x7373 | Tag | RFC 9559, Section 5.1.8.1
0x7384 | SegmentFilename | RFC 9559, Section 5.1.2.2
0x73A4 | SegmentUUID | RFC 9559, Section 5.1.2.1
0x73C4 | ChapterUID | RFC 9559, Section 5.1.7.1.4.1
0x73C5 | TrackUID | RFC 9559, Section 5.1.4.1.2
0x7446 | AttachmentLink | RFC 9559, Section 5.1.4.1.24
0x75A1 | BlockAdditions | RFC 9559, Section 5.1.3.5.2
0x75A2 | DiscardPadding | RFC 9559, Section 5.1.3.5.7
0x7670 | Projection | RFC 9559, Section 5.1.4.1.28.41
0x7671 | ProjectionType | RFC 9559, Section 5.1.4.1.28.42
0x7672 | ProjectionPrivate | RFC 9559, Section 5.1.4.1.28.43
0x7673 | ProjectionPoseYaw | RFC 9559, Section 5.1.4.1.28.44
0x7674 | ProjectionPosePitch | RFC 9559, Section 5.1.4.1.28.45
0x7675 | ProjectionPoseRoll | RFC 9559, Section 5.1.4.1.28.46
0x78B5 | OutputSamplingFrequency | RFC 9559, Section 5.1.4.1.29.2
0x7BA9 | Title | RFC 9559, Section 5.1.2.12
0x7D7B | ChannelPositions | Reclaimed (RFC 9559, Appendix A.27)
0x7FFF | Reserved | RFC 9559
0x010000-0x203FFE | Not valid for use as an Element ID | RFC 9559, Section 27.1
0x22B59C | Language | RFC 9559, Section 5.1.4.1.19
0x22B59D | LanguageBCP47 | RFC 9559, Section 5.1.4.1.20
0x23314F | TrackTimestampScale | RFC 9559, Section 5.1.4.1.15
0x234E7A | DefaultDecodedFieldDuration | RFC 9559, Section 5.1.4.1.14
0x2383E3 | FrameRate | Reclaimed (RFC 9559, Appendix A.26)
0x23E383 | DefaultDuration | RFC 9559, Section 5.1.4.1.13
0x258688 | CodecName | RFC 9559, Section 5.1.4.1.23
0x26B240 | CodecDownloadURL | Reclaimed (RFC 9559, Appendix A.21)
0x2AD7B1 | TimestampScale | RFC 9559, Section 5.1.2.9
0x2EB524 | UncompressedFourCC | RFC 9559, Section 5.1.4.1.28.15
0x2FB523 | GammaValue | Reclaimed (RFC 9559, Appendix A.25)
0x3A9697 | CodecSettings | Reclaimed (RFC 9559, Appendix A.19)
0x3B4040 | CodecInfoURL | Reclaimed (RFC 9559, Appendix A.20)
0x3C83AB | PrevFilename | RFC 9559, Section 5.1.2.4
0x3CB923 | PrevUUID | RFC 9559, Section 5.1.2.3
0x3E83BB | NextFilename | RFC 9559, Section 5.1.2.6
0x3EB923 | NextUUID | RFC 9559, Section 5.1.2.5
0x3FFFFF | Reserved | RFC 9559
0x01000000-0x101FFFFE | Not valid for use as an Element ID | RFC 9559, Section 27.1
0x1043A770 | Chapters | RFC 9559, Section 5.1.7
0x114D9B74 | SeekHead | RFC 9559, Section 5.1.1
0x1254C367 | Tags | RFC 9559, Section 5.1.8
0x1549A966 | Info | RFC 9559, Section 5.1.2
0x1654AE6B | Tracks | RFC 9559, Section 5.1.4
0x18538067 | Segment | RFC 9559, Section 5.1
0x1941A469 | Attachments | RFC 9559, Section 5.1.6
0x1C53BB6B | Cues | RFC 9559, Section 5.1.5
0x1F43B675 | Cluster | RFC 9559, Section 5.1.3
0x1FFFFFFF | Reserved | RFC 9559

### 27.2. Matroska Compression Algorithms Registry

IANA has created a new registry called the "Matroska Compression Algorithms" registry. The values correspond to the unsigned integer `ContentCompAlgo` value described in Section 5.1.4.1.31.6.¶

To register a new Compression Algorithm in this registry, one needs a Compression Algorithm value, a description, a Change Controller, and a Reference to a document describing the Compression Algorithm.¶

The Compression Algorithms are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 4-18446744073709551615.¶

Table 54 shows the initial contents of the "Matroska Compression Algorithms" registry. The Change Controller for the initial entries is the IETF.¶

Table 54: Initial Contents of "Matroska Compression Algorithms" Registry
Compression Algorithm | Description | Reference
--- | --- | ---
0 | zlib | RFC 9559, Section 5.1.4.1.31.6
1 | bzlib | RFC 9559, Section 5.1.4.1.31.6
2 | lzo1x | RFC 9559, Section 5.1.4.1.31.6
3 | Header Stripping | RFC 9559, Section 5.1.4.1.31.6

### 27.3. Matroska Encryption Algorithms Registry

IANA has created a new registry called the "Matroska Encryption Algorithms" registry. The values correspond to the unsigned integer `ContentEncAlgo` value described in Section 5.1.4.1.31.9.¶

To register a new Encryption Algorithm in this registry, one needs an Encryption Algorithm value, a description, a Change Controller, and an optional Reference to a document describing the Encryption Algorithm.¶

The Encryption Algorithms are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 6-18446744073709551615.¶

Table 55 shows the initial contents of the "Matroska Encryption Algorithms" registry. The Change Controller for the initial entries is the IETF.¶

Table 55: Initial Contents of "Matroska Encryption Algorithms" Registry
Encryption Algorithm | Description | Reference
--- | --- | ---
0 | Not encrypted | RFC 9559, Section 5.1.4.1.31.9
1 | DES | RFC 9559, Section 5.1.4.1.31.9
2 | 3DES | RFC 9559, Section 5.1.4.1.31.9
3 | Twofish | RFC 9559, Section 5.1.4.1.31.9
4 | Blowfish | RFC 9559, Section 5.1.4.1.31.9
5 | AES | RFC 9559, Section 5.1.4.1.31.9

### 27.4. Matroska AES Cipher Modes Registry

IANA has created a new registry called the "Matroska AES Cipher Modes" registry. The values correspond to the unsigned integer `AESSettingsCipherMode` value described in Section 5.1.4.1.31.12.¶

To register a new AES Cipher Mode in this registry, one needs an AES Cipher Mode value, a description, a Change Controller, and an optional Reference to a document describing the AES Cipher Mode.¶

The AES Cipher Modes are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 3-18446744073709551615.¶

The value 0 is not valid for use as an AES Cipher Mode.¶

Table 56 shows the initial contents of the "Matroska AES Cipher Modes" registry. The Change Controller for the initial entries is the IETF.¶

Table 56: Initial Contents of "Matroska AES Cipher Modes" Registry
AES Cipher Mode | Description | Reference
--- | --- | ---
0 | Not valid for use as an AES Cipher Mode | RFC 9559, Section 5.1.4.1.31.12
1 | AES-CTR | RFC 9559, Section 5.1.4.1.31.12
2 | AES-CBC | RFC 9559, Section 5.1.4.1.31.12

### 27.5. Matroska Content Encoding Scopes Registry

IANA has created a new registry called the "Matroska Content Encoding Scopes" registry. The values correspond to the unsigned integer `ContentEncodingScope` value described in Section 5.1.4.1.31.3.¶

To register a new Content Encoding Scope in this registry, one needs a Content Encoding Scope value, a description, a Change Controller, and a Reference to a document describing the Content Encoding Scope.¶

The Content Encoding Scopes are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 0x8-0x8000000000000000.¶

The Content Encoding Scope is a bit-field value, so only power of 2 values can be registered.¶

The value 0 is not valid for use as a Content Encoding Scope.¶

Table 57 shows the initial contents of the "Matroska Content Encoding Scopes" registry. The Change Controller for the initial entries is the IETF.¶

Table 57: Initial Contents of "Matroska Content Encoding Scopes" Registry
Content Encoding Scope | Description | Reference
--- | --- | ---
0x0 | Not valid for use as a Content Encoding Scope | RFC 9559, Section 5.1.4.1.31.3
0x1 | Block | RFC 9559, Section 5.1.4.1.31.3
0x2 | Private | RFC 9559, Section 5.1.4.1.31.3
0x4 | Next | RFC 9559, Section 5.1.4.1.31.3

### 27.6. Matroska Content Encoding Types Registry

IANA has created a new registry called the "Matroska Content Encoding Types" registry. The values correspond to the unsigned integer `ContentEncodingType` value described in Section 5.1.4.1.31.4.¶

To register a new Content Encoding Type in this registry, one needs a Content Encoding Type value, a description, a Change Controller, and a Reference to a document describing the Content Encoding Type.¶

The Content Encoding Types are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 2-18446744073709551615.¶

Table 58 shows the initial contents of the "Matroska Content Encoding Types" registry. The Change Controller for the initial entries is the IETF.¶

Table 58: Initial Contents of "Matroska Content Encoding Types" Registry
Content Encoding Type | Description | Reference
--- | --- | ---
0 | Compression | RFC 9559, Section 5.1.4.1.31.4
1 | Encryption | RFC 9559, Section 5.1.4.1.31.4

### 27.7. Matroska Stereo Modes Registry

IANA has created a new registry called the "Matroska Stereo Modes" registry. The values correspond to the unsigned integer `StereoMode` value described in Section 5.1.4.1.28.3.¶

To register a new Stereo Mode in this registry, one needs a Stereo Mode value, a description, a Change Controller, and a Reference to a document describing the Stereo Mode.¶

The Stereo Modes are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 15-18446744073709551615.¶

Table 59 shows the initial contents of the "Matroska Stereo Modes" registry. The Change Controller for the initial entries is the IETF.¶

Table 59: Initial Contents of "Matroska Stereo Modes" Registry
Stereo Mode | Description | Reference
--- | --- | ---
0 | mono | RFC 9559, Section 5.1.4.1.28.3
1 | side by side (left eye first) | RFC 9559, Section 5.1.4.1.28.3
2 | top - bottom (right eye is first) | RFC 9559, Section 5.1.4.1.28.3
3 | top - bottom (left eye is first) | RFC 9559, Section 5.1.4.1.28.3
4 | checkboard (right eye is first) | RFC 9559, Section 5.1.4.1.28.3
5 | checkboard (left eye is first) | RFC 9559, Section 5.1.4.1.28.3
6 | row interleaved (right eye is first) | RFC 9559, Section 5.1.4.1.28.3
7 | row interleaved (left eye is first) | RFC 9559, Section 5.1.4.1.28.3
8 | column interleaved (right eye is first) | RFC 9559, Section 5.1.4.1.28.3
9 | column interleaved (left eye is first) | RFC 9559, Section 5.1.4.1.28.3
10 | anaglyph (cyan/red) | RFC 9559, Section 5.1.4.1.28.3
11 | side by side (right eye first) | RFC 9559, Section 5.1.4.1.28.3
12 | anaglyph (green/magenta) | RFC 9559, Section 5.1.4.1.28.3
13 | both eyes laced in one Block (left eye is first) | RFC 9559, Section 5.1.4.1.28.3
14 | both eyes laced in one Block (right eye is first) | RFC 9559, Section 5.1.4.1.28.3

### 27.8. Matroska Alpha Modes Registry

IANA has created a new registry called the "Matroska Alpha Modes" registry. The values correspond to the unsigned integer `AlphaMode` value described in Section 5.1.4.1.28.4.¶

To register a new Alpha Mode in this registry, one needs an Alpha Mode value, a description, a Change Controller, and an optional Reference to a document describing the Alpha Mode.¶

The Alpha Modes are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 2-18446744073709551615.¶

Table 60 shows the initial contents of the "Matroska Alpha Modes" registry. The Change Controller for the initial entries is the IETF.¶

Table 60: Initial Contents of "Matroska Alpha Modes" Registry
Alpha Mode | Description | Reference
--- | --- | ---
0 | none | RFC 9559, Section 5.1.4.1.28.4
1 | present | RFC 9559, Section 5.1.4.1.28.4

### 27.9. Matroska Display Units Registry

IANA has created a new registry called the "Matroska Display Units" registry. The values correspond to the unsigned integer `DisplayUnit` value described in Section 5.1.4.1.28.14.¶

To register a new Display Unit in this registry, one needs a Display Unit value, a description, a Change Controller, and a Reference to a document describing the Display Unit.¶

The Display Units are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 5-18446744073709551615.¶

Table 61 shows the initial contents of the "Matroska Display Units" registry. The Change Controller for the initial entries is the IETF.¶

Table 61: Initial Contents of "Matroska Display Units" Registry
Display Unit | Description | Reference
--- | --- | ---
0 | pixels | RFC 9559, Section 5.1.4.1.28.14
1 | centimeters | RFC 9559, Section 5.1.4.1.28.14
2 | inches | RFC 9559, Section 5.1.4.1.28.14
3 | display aspect ratio | RFC 9559, Section 5.1.4.1.28.14
4 | unknown | RFC 9559, Section 5.1.4.1.28.14

### 27.10. Matroska Horizontal Chroma Sitings Registry

IANA has created a new registry called the "Matroska Horizontal Chroma Sitings" registry. The values correspond to the unsigned integer `ChromaSitingHorz` value described in Section 5.1.4.1.28.23.¶

To register a new Horizontal Chroma Siting in this registry, one needs a Horizontal Chroma Siting value, a description, a Change Controller, and an optional Reference to a document describing the Horizontal Chroma Siting.¶

The Horizontal Chroma Sitings are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 3-18446744073709551615.¶

Table 62 shows the initial contents of the "Matroska Horizontal Chroma Sitings" registry. The Change Controller for the initial entries is the IETF.¶

Table 62: Initial Contents of "Matroska Horizontal Chroma Sitings" Registry
Horizontal Chroma Siting | Description | Reference
--- | --- | ---
0 | unspecified | RFC 9559, Section 5.1.4.1.28.23
1 | left collocated | RFC 9559, Section 5.1.4.1.28.23
2 | half | RFC 9559, Section 5.1.4.1.28.23

### 27.11. Matroska Vertical Chroma Sitings Registry

IANA has created a new registry called the "Matroska Vertical Chroma Sitings" registry. The values correspond to the unsigned integer `ChromaSitingVert` value described in Section 5.1.4.1.28.24.¶

To register a new Vertical Chroma Siting in this registry, one needs a Vertical Chroma Siting value, a description, a Change Controller, and an optional Reference to a document describing the Vertical Chroma Siting.¶

The Vertical Chroma Sitings are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 3-18446744073709551615.¶

Table 63 shows the initial contents of the "Matroska Vertical Chroma Sitings" registry. The Change Controller for the initial entries is the IETF.¶

Table 63: Initial Contents of "Matroska Vertical Chroma Sitings" Registry
Vertical Chroma Siting | Description | Reference
--- | --- | ---
0 | unspecified | RFC 9559, Section 5.1.4.1.28.24
1 | top collocated | RFC 9559, Section 5.1.4.1.28.24
2 | half | RFC 9559, Section 5.1.4.1.28.24

### 27.12. Matroska Color Ranges Registry

IANA has created a new registry called the "Matroska Color Ranges" registry. The values correspond to the unsigned integer `Range` value described in Section 5.1.4.1.28.25.¶

To register a new Color Range in this registry, one needs a Color Range value, a description, a Change Controller, and a Reference to a document describing the Color Range.¶

The Color Ranges are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 4-18446744073709551615.¶

Table 64 shows the initial contents of the "Matroska Color Ranges" registry. The Change Controller for the initial entries is the IETF.¶

Table 64: Initial Contents of "Matroska Color Ranges" Registry
Color Range | Description | Reference
--- | --- | ---
0 | unspecified | RFC 9559, Section 5.1.4.1.28.25
1 | broadcast range | RFC 9559, Section 5.1.4.1.28.25
2 | full range (no clipping) | RFC 9559, Section 5.1.4.1.28.25
3 | defined by MatrixCoefficients / TransferCharacteristics | RFC 9559, Section 5.1.4.1.28.25

### 27.13. Matroska Tags Target Types Registry

IANA has created a new registry called the "Matroska Tags Target Types" registry. The values correspond to the unsigned integer `TargetTypeValue` value described in Section 5.1.8.1.1.1.¶

To register a new Tags Target Type in this registry, one needs a Tags Target Type value, a description, a Change Controller, and a Reference to a document describing the Tags Target Type.¶

The Tags Target Types are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 1-9, 11-19, 21-29, 31-39, 41-49, 51-59, 61-69, and 71-18446744073709551615.¶

The value 0 is not valid for use as a Tags Target Type.¶

Table 65 shows the initial contents of the "Matroska Tags Target Types" registry. The Change Controller for the initial entries is the IETF.¶

Table 65: Initial Contents of "Matroska Tags Target Types" Registry
Tags Target Type | Description | Reference
--- | --- | ---
70 | COLLECTION | RFC 9559, Section 5.1.8.1.1.1
60 | EDITION / ISSUE / VOLUME / OPUS / SEASON / SEQUEL | RFC 9559, Section 5.1.8.1.1.1
50 | ALBUM / OPERA / CONCERT / MOVIE / EPISODE | RFC 9559, Section 5.1.8.1.1.1
40 | PART / SESSION | RFC 9559, Section 5.1.8.1.1.1
30 | TRACK / SONG / CHAPTER | RFC 9559, Section 5.1.8.1.1.1
20 | SUBTRACK / MOVEMENT / SCENE | RFC 9559, Section 5.1.8.1.1.1
10 | SHOT | RFC 9559, Section 5.1.8.1.1.1
0 | Not valid for use as a Tags Target Type | RFC 9559, Section 5.1.8.1.1.1

### 27.14. Matroska Chapter Codec IDs Registry

IANA has created a new registry called the "Matroska Chapter Codec IDs" registry. The values correspond to the unsigned integer `ChapProcessCodecID`, `ChapterTranslateCodec`, and `TrackTranslateCodec` values described in Section 5.1.7.1.4.15.¶

To register a new Chapter Codec ID in this registry, one needs a Chapter Codec ID value, a description, a Change Controller, and a Reference to a document describing the Chapter Codec ID.¶

The Chapter Codec IDs are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 2-18446744073709551615.¶

Table 66 shows the initial contents of the "Matroska Chapter Codec IDs" registry. The Change Controller for the initial entries is the IETF.¶

Table 66: Initial Contents of "Matroska Chapter Codec IDs" Registry
Chapter Codec ID | Description | Reference
--- | --- | ---
0 | Matroska Script | RFC 9559, Section 5.1.7.1.4.15
1 | DVD-menu | RFC 9559, Section 5.1.7.1.4.15

### 27.15. Matroska Projection Types Registry

IANA has created a new registry called the "Matroska Projection Types" registry. The values correspond to the unsigned integer `ProjectionType` value described in Section 5.1.4.1.28.42.¶

To register a new Projection Type in this registry, one needs a Projection Type value, a description, a Change Controller, and an optional Reference to a document describing the Projection Type.¶

The Projection Types are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 4-18446744073709551615.¶

Table 67 shows the initial contents of the "Matroska Projection Types" registry. The Change Controller for the initial entries is the IETF.¶

Table 67: Initial Contents of "Matroska Projection Types" Registry
Projection Type | Description | Reference
--- | --- | ---
0 | rectangular | RFC 9559, Section 5.1.4.1.28.42
1 | equirectangular | RFC 9559, Section 5.1.4.1.28.42
2 | cubemap | RFC 9559, Section 5.1.4.1.28.42
3 | mesh | RFC 9559, Section 5.1.4.1.28.42

### 27.16. Matroska Track Types Registry

IANA has created a new registry called the "Matroska Track Types" registry. The values correspond to the unsigned integer `TrackType` value described in Section 5.1.4.1.3.¶

To register a new Track Type in this registry, one needs a Track Type value, a description, a Change Controller, and a Reference to a document describing the Track Type.¶

The Track Types are to be allocated according to the "Specification Required" policy [RFC8126]. Available values range from 4-15, 19-31, and 34-18446744073709551615.¶

The value 0 is not valid for use as a Track Type.¶

Table 68 shows the initial contents of the "Matroska Track Types" registry. The Change Controller for the initial entries is the IETF.¶

Table 68: Initial Contents of "Matroska Track Types" Registry
Track Type | Description | Reference
--- | --- | ---
0 | Not valid for use as a Track Type | RFC 9559, Section 5.1.4.1.3
1 | video | RFC 9559, Section 5.1.4.1.3
2 | audio | RFC 9559, Section 5.1.4.1.3
3 | complex | RFC 9559, Section 5.1.4.1.3
16 | logo | RFC 9559, Section 5.1.4.1.3
17 | subtitle | RFC 9559, Section 5.1.4.1.3
18 | buttons | RFC 9559, Section 5.1.4.1.3
32 | control | RFC 9559, Section 5.1.4.1.3
33 | metadata | RFC 9559, Section 5.1.4.1.3

### 27.17. Matroska Track Plane Types Registry

IANA has created a new registry called the "Matroska Track Plane Types" registry. The values correspond to the unsigned integer `TrackPlaneType` value described in Section 5.1.4.1.30.4.¶

To register a new Track Plane Type in this registry, one needs a Track Plane Type value, a description, a Change Controller, and an optional Reference to a document describing the Track Plane Type.¶

The Track Plane Types are to be allocated according to the "First Come First Served" policy [RFC8126]. Available values range from 3-18446744073709551615.¶

Table 69 shows the initial contents of the "Matroska Track Plane Types" registry. The Change Controller for the initial entries is the IETF.¶

Table 69: Initial Contents of "Matroska Track Plane Types" Registry
Track Plane Type | Description | Reference
--- | --- | ---
0 | left eye | RFC 9559, Section 5.1.4.1.30.4
1 | right eye | RFC 9559, Section 5.1.4.1.30.4
2 | background | RFC 9559, Section 5.1.4.1.30.4

### 27.18. Media Types

Matroska files and streams are found in three main forms: audio-video, audio-only, and (occasionally) stereoscopic video.¶

Historically, Matroska files and streams have used the following media types with an "x-" prefix. For better compatibility, a system SHOULD be able to handle both formats. Newer systems SHOULD NOT use the historic format and use the format that follows the format in [RFC6838] instead.¶

IANA has registered three media types per the templates (see [RFC6838]) in the following subsections.¶

#### 27.18.1. For Files Containing Video Tracks

Type name:
  video¶
Subtype name:
  matroska¶
Required parameters:
  N/A¶
Optional parameters:
  N/A¶
Encoding considerations:
  As per RFCs 9559 and 8794¶
Security considerations:
  See Section 26 of RFC 9559.¶
Interoperability considerations:
  Due to the extensibility of Matroska, it is possible to encounter files with unknown but valid EBML Elements. Readers should be ready to handle this case. The fixed byte order, octet boundaries, and UTF-8 usage allow for broad interoperability.¶
Published specification:
  RFC 9559¶
Applications that use this media type:
  FFmpeg, VLC, etc.¶
Fragment identifier considerations:

  N/A¶

Additional information:

  Deprecated alias names for this type:
    video/x-matroska¶
  Magic number(s):
    N/A¶
  File extension(s):
    mkv¶
  Macintosh file type code(s):
    N/A¶
Person & email address to contact for further information:
  IETF CELLAR WG (cellar@ietf.org)¶
Intended usage:
  COMMON¶
Restrictions on usage:
  None¶
Author:
  IETF CELLAR WG¶
Change controller:
  IETF¶

#### 27.18.2. For Files Containing Audio Tracks with No Video Tracks

Type name:
  audio¶
Subtype name:
  matroska¶
Required parameters:
  N/A¶
Optional parameters:
  N/A¶
Encoding considerations:
  As per RFCs 9559 and 8794¶
Security considerations:
  See Section 26 of RFC 9559.¶
Interoperability considerations:
  Due to the extensibility of Matroska, it is possible to encounter files with unknown but valid EBML Elements. Readers should be ready to handle this case. The fixed byte order, octet boundaries, and UTF-8 usage allow for broad interoperability.¶
Published specification:
  RFC 9559¶
Applications that use this media type:
  FFmpeg, VLC, etc.¶
Fragment identifier considerations:
  N/A¶
Additional information:

  Deprecated alias names for this type:
    audio/x-matroska¶
  Magic number(s):
    N/A¶
  File extension(s):
    mka¶
  Macintosh file type code(s):
    N/A¶
Person & email address to contact for further information:
  IETF CELLAR WG (cellar@ietf.org)¶
Intended usage:
  COMMON¶
Restrictions on usage:
  None¶
Author:
  IETF CELLAR WG¶
Change controller:
  IETF¶

#### 27.18.3. For Files Containing a Stereoscopic Video Track

Type name:
  video¶
Subtype name:
  matroska-3d¶
Required parameters:
  N/A¶
Optional parameters:
  N/A¶
Encoding considerations:
  As per RFCs 9559 and 8794¶
Security considerations:
  See Section 26 of RFC 9559.¶
Interoperability considerations:
  Due to the extensibility of Matroska, it is possible to encounter files with unknown but valid EBML Elements. Readers should be ready to handle this case. The fixed byte order, octet boundaries, and UTF-8 usage allow for broad interoperability.¶
Published specification:
  RFC 9559¶
Applications that use this media type:
  FFmpeg, VLC, etc.¶
Fragment identifier considerations:
  N/A¶
Additional information:

  Deprecated alias names for this type:
    video/x-matroska-3d¶
  Magic number(s):
    N/A¶
  File extension(s):
    mk3d¶
  Macintosh file type code(s):
    N/A¶
Person & email address to contact for further information:
  IETF CELLAR WG (cellar@ietf.org)¶
Intended usage:
  COMMON¶
Restrictions on usage:
  None¶
Author:
  IETF CELLAR WG¶
Change controller:
  IETF¶

## 28. References

### 28.1. Normative References

[CIE-1931]
  Wikipedia, "CIE 1931 color space", <https://en.wikipedia.org/w/index.php?title=CIE_1931_color_space&oldid=1242811504>.
[ISO639-2]
  International Organization for Standardization, "Codes for the Representation of Names of Languages", ISO 639-2, December 2017, <https://www.loc.gov/standards/iso639-2/php/code_list.php>.
[ISO9899]
  International Organization for Standardization, "Information technology -- Programming languages -- C", ISO/IEC 9899:2018, June 2018, <https://www.iso.org/standard/74528.html>.
[ITU-H.273]
  ITU-T, "Coding-independent code points for video signal type identification", ITU-T Recommendation H.273, September 2023, <https://www.itu.int/rec/T-REC-H.273-202309-P/en>.
[RFC1950]
  Deutsch, P. and J. Gailly, "ZLIB Compressed Data Format Specification version 3.3", RFC 1950, DOI 10.17487/RFC1950, May 1996, <https://www.rfc-editor.org/info/rfc1950>.
[RFC2119]
  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>.
[RFC5646]
  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, September 2009, <https://www.rfc-editor.org/info/rfc5646>.
[RFC6838]
  Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013, <https://www.rfc-editor.org/info/rfc6838>.
[RFC8081]
  Lilley, C., "The "font" Top-Level Media Type", RFC 8081, DOI 10.17487/RFC8081, February 2017, <https://www.rfc-editor.org/info/rfc8081>.
[RFC8126]
  Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174]
  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8794]
  Lhomme, S., Rice, D., and M. Bunkus, "Extensible Binary Meta Language", RFC 8794, DOI 10.17487/RFC8794, July 2020, <https://www.rfc-editor.org/info/rfc8794>.
[RFC9562]
  Davis, K., Peabody, B., and P. Leach, "Universally Unique IDentifiers (UUIDs)", RFC 9562, DOI 10.17487/RFC9562, May 2024, <https://www.rfc-editor.org/info/rfc9562>.

### 28.2. Informative References

[AVIFormat]
  Microsoft Corporation, "AVI RIFF File Reference", June 2023, <https://docs.microsoft.com/en-us/windows/win32/directshow/avi-riff-file-reference>.
[Blowfish]
  Schneier, B., "The Blowfish Encryption Algorithm", 1993, <https://www.schneier.com/academic/blowfish/>.
[BZIP2]
  Seward, J., "bzip2", July 2019, <https://sourceware.org/bzip2/>.
[DivXTrickTrack]
  "Smooth FF/RW", December 2010, <https://web.archive.org/web/20101222001148/http://labs.divx.com/node/16601>.
[DivXWorldFonts]
  "World Fonts", December 2010, <https://web.archive.org/web/20110214132246/http://labs.divx.com/node/16602>.
[DVD-Video]
  DVD Forum, "DVD-Books: Part 3 DVD-Video Book", November 1995, <http://www.dvdforum.org/>.
[Err7189]
  RFC Errata, Erratum ID 7189, RFC 8794, <https://www.rfc-editor.org/errata/eid7189>.
[Err7191]
  RFC Errata, Erratum ID 7191, RFC 8794, <https://www.rfc-editor.org/errata/eid7191>.
[FIPS197]
  National Institute of Standards and Technology (NIST), "Advanced Encryption Standard (AES)", FIPS PUB 197, DOI 10.6028/NIST.FIPS.197, November 2001, <https://csrc.nist.gov/publications/detail/fips/197/final>.
[FIPS46-3]
  National Institute of Standards and Technology (NIST), "Data Encryption Standard (DES)", FIPS PUB 46, October 1999, <https://csrc.nist.gov/publications/detail/fips/46/3/archive/1999-10-25>.
[FourCC-RGB]
  FOURCC, "RGB pixel formats", <https://web.archive.org/web/20160609214806/https://www.fourcc.org/rgb.php>.
[FourCC-YUV]
  FOURCC, "YUV pixel formats", <https://web.archive.org/web/20160609214806/https://www.fourcc.org/yuv.php>.
[JPEG]
  ITU-T, "INFORMATION TECHNOLOGY - DIGITAL COMPRESSION AND CODING OF CONTINUOUS-TONE STILL IMAGES - REQUIREMENTS AND GUIDELINES", ITU-T Recommendation T.81, September 1992, <https://www.w3.org/Graphics/JPEG/itu-t81.pdf>.
[libmatroska]
  "libmatroska", March 2024, <https://github.com/Matroska-Org/libmatroska>.
[LZO]
  Tarreau, W. and R. Rodgman, "LZO stream format as understood by Linux's LZO decompressor", October 2018, <https://www.kernel.org/doc/Documentation/lzo.txt>.
[MatroskaCodec]
  Lhomme, S., Bunkus, M., and D. Rice, "Matroska Media Container Codec Specifications", Work in Progress, Internet-Draft, draft-ietf-cellar-codec-13, 5 May 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-cellar-codec-13>.
[MatroskaTags]
  Lhomme, S., Bunkus, M., and D. Rice, "Matroska Media Container Tag Specifications", Work in Progress, Internet-Draft, draft-ietf-cellar-tags-13, 5 May 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-cellar-tags-13>.
[MCF]
  "MCF specification, introduction", <http://mukoli.free.fr/mcf/>.
[MSRGB]
  Microsoft Corporation, "Compression Enumeration", June 2021, <https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-wmf/4e588f70-bd92-4a6f-b77f-35d0feaf7a57>.
[MSYUV16]
  Microsoft Corporation, "10-bit and 16-bit YUV Video Formats", November 2022, <https://learn.microsoft.com/en-us/windows/win32/medfound/10-bit-and-16-bit-yuv-video-formats>.
[MSYUV8]
  Microsoft Corporation, "Recommended 8-Bit YUV Formats for Video Rendering", January 2021, <https://learn.microsoft.com/en-us/windows/win32/medfound/recommended-8-bit-yuv-formats-for-video-rendering>.
[RFC0959]
  Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985, <https://www.rfc-editor.org/info/rfc959>.
[RFC2083]
  Boutell, T., "PNG (Portable Network Graphics) Specification Version 1.0", RFC 2083, DOI 10.17487/RFC2083, March 1997, <https://www.rfc-editor.org/info/rfc2083>.
[RFC3533]
  Pfeiffer, S., "The Ogg Encapsulation Format Version 0", RFC 3533, DOI 10.17487/RFC3533, May 2003, <https://www.rfc-editor.org/info/rfc3533>.
[RFC4732]
  Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet Denial-of-Service Considerations", RFC 4732, DOI 10.17487/RFC4732, December 2006, <https://www.rfc-editor.org/info/rfc4732>.
[RFC9110]
  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, Ed., "HTTP Semantics", STD 97, RFC 9110, DOI 10.17487/RFC9110, June 2022, <https://www.rfc-editor.org/info/rfc9110>.
[SMB-CIFS]
  Microsoft Corporation, "[MS-CIFS]: Common Internet File System (CIFS) Protocol", October 2020, <https://winprotocoldoc.blob.core.windows.net/productionwindowsarchives/MS-CIFS/%5bMS-CIFS%5d.pdf>.
[SP800-38A]
  National Institute of Standards and Technology (NIST), "Recommendation for Block Cipher Modes of Operation: Methods and Techniques", DOI 10.6028/NIST.SP.800-38A, NIST Special Publication 800-38A, December 2001, <https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf>.
[SP800-67]
  National Institute of Standards and Technology (NIST), "Recommendation for the Triple Data Encryption Algorithm (TDEA) Block Cipher", DOI 10.6028/NIST.SP.800-67r2, NIST Special Publication 800-67, November 2017, <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-67r2.pdf>.
[Twofish]
  Schneier, B., Kelsey, J., Whiting, D., Wagner, D., Hall, C., and N. Ferguson, "Twofish: A 128-Bit Block Cipher", June 1998, <https://www.schneier.com/academic/archives/1998/06/twofish_a_128-bit_bl.html>.
[WebM-Enc]
  Galligan, F., "WebM Encryption", September 2016, <https://www.webmproject.org/docs/webm-encryption/>.
[WebVTT]
  Pieters, S., Pfeiffer, S., Ed., Jaegenstedt, P., and I. Hickson, "WebVTT: The Web Video Text Tracks Format", W3C Candidate Recommendation, April 2019, <https://www.w3.org/TR/2019/CR-webvtt1-20190404/>.

## Appendix A. Historic Deprecated Elements

As Matroska has evolved since 2002, many parts that were considered for use in the format were never used and often incorrectly designed. Many of the elements that were defined then are not found in any known files but were part of public specs. DivX also had a few custom elements that were designed for custom features.¶

In this appendix, we list elements that have a known ID that SHOULD NOT be reused to avoid colliding with existing files. These might be reassigned by IANA in the future if there are no more IDs for a given size. A short description of what each ID was used for is included, but the text is not normative.¶

### A.1. SilentTracks Element

type / id:
  master / 0x5854¶
path:
  `\Segment\Cluster\SilentTracks`¶
documentation:
  The list of tracks that are not used in that part of the stream. It is useful when using overlay tracks for seeking or deciding what track to use.¶

### A.2. SilentTrackNumber Element

type / id:
  uinteger / 0x58D7¶
path:
  `\Segment\Cluster\SilentTracks\SilentTrackNumber`¶
documentation:
  One of the track numbers that is not used from now on in the stream. It could change later if not specified as silent in a further `Cluster`.¶

### A.3. BlockVirtual Element

type / id:
  binary / 0xA2¶
path:
  `\Segment\Cluster\BlockGroup\BlockVirtual`¶
documentation:
  A `Block` with no data. It must be stored in the stream at the place the real `Block` would be in display order.¶

### A.4. ReferenceVirtual Element

type / id:
  integer / 0xFD¶
path:
  `\Segment\Cluster\BlockGroup\ReferenceVirtual`¶
documentation:
  The `Segment Position` of the data that would otherwise be in position of the virtual block.¶

### A.5. Slices Element

type / id:
  master / 0x8E¶
path:
  `\Segment\Cluster\BlockGroup\Slices`¶
documentation:
  Contains slices description.¶

### A.6. TimeSlice Element

type / id:
  master / 0xE8¶
path:
  `\Segment\Cluster\BlockGroup\Slices\TimeSlice`¶
documentation:
  Contains extra time information about the data contained in the `Block`. Being able to interpret this element is not required for playback.¶

### A.7. LaceNumber Element

type / id:
  uinteger / 0xCC¶
path:
  `\Segment\Cluster\BlockGroup\Slices\TimeSlice\LaceNumber`¶
documentation:
  The reverse number of the frame in the lace (0 is the last frame, 1 is the next to last, etc.). Being able to interpret this element is not required for playback.¶

### A.8. FrameNumber Element

type / id:
  uinteger / 0xCD¶
path:
  `\Segment\Cluster\BlockGroup\Slices\TimeSlice\FrameNumber`¶
documentation:
  The number of the frame to generate from this lace with this delay (allows for the generation of many frames from the same Block/Frame).¶

### A.9. BlockAdditionID Element

type / id:
  uinteger / 0xCB¶
path:
  `\Segment\Cluster\BlockGroup\Slices\TimeSlice\BlockAdditionID`¶
documentation:
  The ID of the `BlockAdditional` element (0 is the main `Block`).¶

### A.10. Delay Element

type / id:
  uinteger / 0xCE¶
path:
  `\Segment\Cluster\BlockGroup\Slices\TimeSlice\Delay`¶
documentation:
  The delay to apply to the element, expressed in Track Ticks; see Section 11.1.¶

### A.11. SliceDuration Element

type / id:
  uinteger / 0xCF¶
path:
  `\Segment\Cluster\BlockGroup\Slices\TimeSlice\SliceDuration`¶
documentation:
  The duration to apply to the element, expressed in Track Ticks; see Section 11.1.¶

### A.12. ReferenceFrame Element

type / id:
  master / 0xC8¶
path:
  `\Segment\Cluster\BlockGroup\ReferenceFrame`¶
documentation:
  Contains information about the last reference frame. See [DivXTrickTrack].¶

### A.13. ReferenceOffset Element

type / id:
  uinteger / 0xC9¶
path:
  `\Segment\Cluster\BlockGroup\ReferenceFrame\ReferenceOffset`¶
documentation:
  The relative offset, in bytes, from the previous `BlockGroup` element for this Smooth FF/RW video track to the containing `BlockGroup` element. See [DivXTrickTrack].¶

### A.14. ReferenceTimestamp Element

type / id:
  uinteger / 0xCA¶
path:
  `\Segment\Cluster\BlockGroup\ReferenceFrame\ReferenceTimestamp`¶
documentation:
  The timestamp of the `BlockGroup` pointed to by ReferenceOffset, expressed in Track Ticks; see Section 11.1. See [DivXTrickTrack].¶

### A.15. EncryptedBlock Element

type / id:
  binary / 0xAF¶
path:
  `\Segment\Cluster\EncryptedBlock`¶
documentation:
  Similar to `SimpleBlock` (see Section 10.2), but the data inside the `Block` are Transformed (encrypted and/or signed).¶

### A.16. MinCache Element

type / id:
  uinteger / 0x6DE7¶
path:
  `\Segment\Tracks\TrackEntry\MinCache`¶
documentation:
  The minimum number of frames a player should be able to cache during playback. If set to 0, the reference pseudo-cache system is not used.¶

### A.17. MaxCache Element

type / id:
  uinteger / 0x6DF8¶
path:
  `\Segment\Tracks\TrackEntry\MaxCache`¶
documentation:
  The maximum cache size necessary to store referenced frames in and the current frame. 0 means no cache is needed.¶

### A.18. TrackOffset Element

type / id:
  integer / 0x537F¶
path:
  `\Segment\Tracks\TrackEntry\TrackOffset`¶
documentation:
  A value to add to the `Block`'s Timestamp, expressed in Matroska Ticks -- i.e., in nanoseconds; see Section 11.1. This can be used to adjust the playback offset of a track.¶

### A.19. CodecSettings Element

type / id:
  utf-8 / 0x3A9697¶
path:
  `\Segment\Tracks\TrackEntry\CodecSettings`¶
documentation:
  A string describing the encoding setting used.¶

### A.20. CodecInfoURL Element

type / id:
  string / 0x3B4040¶
path:
  `\Segment\Tracks\TrackEntry\CodecInfoURL`¶
documentation:
  A URL to find information about the codec used.¶

### A.21. CodecDownloadURL Element

type / id:
  string / 0x26B240¶
path:
  `\Segment\Tracks\TrackEntry\CodecDownloadURL`¶
documentation:
  A URL to download information about the codec used.¶

### A.22. CodecDecodeAll Element

type / id:
  uinteger / 0xAA¶
path:
  `\Segment\Tracks\TrackEntry\CodecDecodeAll`¶
documentation:
  Set to 1 if the codec can decode potentially damaged data.¶

### A.23. TrackOverlay Element

type / id:
  uinteger / 0x6FAB¶
path:
  `\Segment\Tracks\TrackEntry\TrackOverlay`¶
documentation:
  Specify that this track is an overlay track for the `Track` specified (in the u-integer). This means that when this track has a gap on `SilentTracks`, the overlay track should be used instead. The order of multiple `TrackOverlay` matters; the first one is the one that should be used. If the first one is not found, it should be the second, etc.¶

### A.24. AspectRatioType Element

type / id:
  uinteger / 0x54B3¶
path:
  `\Segment\Tracks\TrackEntry\Video\AspectRatioType`¶
documentation:
  Specifies the possible modifications to the aspect ratio.¶

### A.25. GammaValue Element

type / id:
  float / 0x2FB523¶
path:
  `\Segment\Tracks\TrackEntry\Video\GammaValue`¶
documentation:
  Gamma value.¶

### A.26. FrameRate Element

type / id:
  float / 0x2383E3¶
path:
  `\Segment\Tracks\TrackEntry\Video\FrameRate`¶
documentation:
  Number of frames per second. This value is informational only. It is intended for constant frame rate streams and should not be used for a variable frame rate `TrackEntry`.¶

### A.27. ChannelPositions Element

type / id:
  binary / 0x7D7B¶
path:
  `\Segment\Tracks\TrackEntry\Audio\ChannelPositions`¶
documentation:
  Table of horizontal angles for each successive channel.¶

### A.28. TrickTrackUID Element

type / id:
  uinteger / 0xC0¶
path:
  `\Segment\Tracks\TrackEntry\TrickTrackUID`¶
documentation:
  The `TrackUID` of the Smooth FF/RW video in the paired EBML structure corresponding to this video track. See [DivXTrickTrack].¶

### A.29. TrickTrackSegmentUID Element

type / id:
  binary / 0xC1¶
path:
  `\Segment\Tracks\TrackEntry\TrickTrackSegmentUID`¶
documentation:
  The `SegmentUUID` of the `Segment` containing the track identified by TrickTrackUID. See [DivXTrickTrack].¶

### A.30. TrickTrackFlag Element

type / id:
  uinteger / 0xC6¶
path:
  `\Segment\Tracks\TrackEntry\TrickTrackFlag`¶
documentation:
  Set to 1 if this video track is a Smooth FF/RW track. If set to 1, `MasterTrackUID` and `MasterTrackSegUID` should be present, and `BlockGroups` for this track must contain ReferenceFrame structures. Otherwise, TrickTrackUID and TrickTrackSegUID must be present if this track has a corresponding Smooth FF/RW track. See [DivXTrickTrack].¶

### A.31. TrickMasterTrackUID Element

type / id:
  uinteger / 0xC7¶
path:
  `\Segment\Tracks\TrackEntry\TrickMasterTrackUID`¶
documentation:
  The `TrackUID` of the video track in the paired EBML structure that corresponds to this Smooth FF/RW track. See [DivXTrickTrack].¶

### A.32. TrickMasterTrackSegmentUID Element

type / id:
  binary / 0xC4¶
path:
  `\Segment\Tracks\TrackEntry\TrickMasterTrackSegmentUID`¶
documentation:
  The `SegmentUUID` of the `Segment` containing the track identified by MasterTrackUID. See [DivXTrickTrack].¶

### A.33. ContentSignature Element

type / id:
  binary / 0x47E3¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSignature`¶
documentation:
  A cryptographic signature of the contents.¶

### A.34. ContentSigKeyID Element

type / id:
  binary / 0x47E4¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSigKeyID`¶
documentation:
  This is the ID of the private key that the data was signed with.¶

### A.35. ContentSigAlgo Element

type / id:
  uinteger / 0x47E5¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSigAlgo`¶
documentation:
  The algorithm used for the signature.¶

### A.36. ContentSigHashAlgo Element

type / id:
  uinteger / 0x47E6¶
path:
  `\Segment\Tracks\TrackEntry\ContentEncodings\ContentEncoding\ContentEncryption\ContentSigHashAlgo`¶
documentation:
  The hash algorithm used for the signature.¶

### A.37. CueRefCluster Element

type / id:
  uinteger / 0x97¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefCluster`¶
documentation:
  The `Segment Position` of the `Cluster` containing the referenced `Block`.¶

### A.38. CueRefNumber Element

type / id:
  uinteger / 0x535F¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefNumber`¶
documentation:
  Number of the referenced `Block` of Track X in the specified `Cluster`.¶

### A.39. CueRefCodecState Element

type / id:
  uinteger / 0xEB¶
path:
  `\Segment\Cues\CuePoint\CueTrackPositions\CueReference\CueRefCodecState`¶
documentation:
  The `Segment Position` of the Codec State corresponding to this referenced element. 0 means that the data is taken from the initial `TrackEntry`.¶

### A.40. FileReferral Element

type / id:
  binary / 0x4675¶
path:
  `\Segment\Attachments\AttachedFile\FileReferral`¶
documentation:
  A binary value that a track/codec can refer to when the attachment is needed.¶

### A.41. FileUsedStartTime Element

type / id:
  uinteger / 0x4661¶
path:
  `\Segment\Attachments\AttachedFile\FileUsedStartTime`¶
documentation:
  The timestamp at which this optimized font attachment comes into context, expressed in Segment Ticks, which are based on `TimestampScale`. See [DivXWorldFonts].¶

### A.42. FileUsedEndTime Element

type / id:
  uinteger / 0x4662¶
path:
  `\Segment\Attachments\AttachedFile\FileUsedEndTime`¶
documentation:
  The timestamp at which this optimized font attachment goes out of context, expressed in Segment Ticks, which are based on `TimestampScale`. See [DivXWorldFonts].¶

### A.43. TagDefaultBogus Element

type / id:
  uinteger / 0x44B4¶
path:
  `\Segment\Tags\Tag\+SimpleTag\TagDefaultBogus`¶
documentation:
  A variant of the `TagDefault` element with a bogus element ID; see Section 5.1.8.1.2.4.¶

## Authors' Addresses