Matroska Media Container Codec Specifications

Introduction Matroska is a multimedia container format. It stores interleaved and timestamped audio/video/subtitle data using various codecs. To interpret the codec data, a mapping between the way the data is stored in Matroska and how it is understood by such a codec is necessary. This document intends to define this mapping for many commonly used codecs in Matroska.

Status of This Document This document is a work-in-progress specification defining the Matroska file format as part of the IETF Cellar working group. It uses basic elements and concept already defined in the Matroska specifications defined by this workgroup .

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 when, and only when, they appear in all capitals, as shown here.

Codec Mappings A Codec Mapping is a set of attributes to identify, name, and contextualize the format and characteristics of encoded data that can be contained within Matroska Clusters. Each TrackEntry used within Matroska MUST reference a defined Codec Mapping using the Codec ID to identify and describe the format of the encoded data in its associated Clusters. This Codec ID is a unique registered identifier that represents the encoding stored within the Track. Certain encodings MAY also require some form of codec initialization to provide its decoder with context and technical metadata. The intention behind this list is not to list all existing audio and video codecs, but rather to list those codecs that are currently supported in Matroska and therefore need a well defined Codec ID so that all developers supporting Matroska will use the same Codec ID. If you feel we missed support for a very important codec, please tell us on our development mailing list (cellar at ietf.org).

Defining Matroska Codec Support Support for a codec is defined in Matroska with the following values.

Codec ID Each codec supported for storage in Matroska MUST have a unique Codec ID. Each Codec ID MUST be prefixed with the string from the following table according to the associated type of the codec. All characters of a Codec ID Prefix MUST be capital letters (A-Z) except for the last character of a Codec ID Prefix which MUST be an underscore ("_").

Codec Type	Codec ID Prefix
Video	"V_"
Audio	"A_"
Subtitle	"S_"
Button	"B_"

Each Codec ID MUST include a Major Codec ID immediately following the Codec ID Prefix. A Major Codec ID MAY be followed by an OPTIONAL Codec ID Suffix to communicate a refinement of the Major Codec ID. If a Codec ID Suffix is used, then the Codec ID MUST include a forward slash ("/") as a separator between the Major Codec ID and the Codec ID Suffix. The Major Codec ID MUST be composed of only capital letters (A-Z) and numbers (0-9). The Codec ID Suffix MUST be composed of only capital letters (A-Z), numbers (0-9), underscore ("_"), and forward slash ("/"). The following table provides examples of valid Codec IDs and their components:

Codec ID Prefix	Major Codec ID	Separator	Codec ID Suffix	Codec ID
A_	AAC	/	MPEG2/LC/SBR	A_AAC/MPEG2/LC/SBR
V_	MPEG4	/	ISO/ASP	V_MPEG4/ISO/ASP
V_	MPEG1			V_MPEG1

Codec Name Each encoding supported for storage in Matroska MUST have a Codec Name. The Codec Name provides a readable label for the encoding.

Description An optional description for the encoding. This value is only intended for human consumption.

Initialization Each encoding supported for storage in Matroska MUST have a defined Initialization. The Initialization MUST describe the storage of data necessary to initialize the decoder, which MUST be stored within the CodecPrivate Element. When the Initialization is updated within a track, then that updated Initialization data MUST be written into the CodecState Element of the first Cluster to require it. If the encoding does not require any form of Initialization, then none MUST be used to define the Initialization and the CodecPrivate Element SHOULD NOT be written and MUST be ignored. Data that is defined Initialization to be stored in the CodecPrivate Element is known as Private Data.

Codec BlockAdditions Additional data that contextualizes or supplements a Block can be stored within the BlockAdditional Element of a BlockMore Element. This BlockAdditional data MAY be passed to the associated decoder along with the content of the Block Element. Each BlockAdditional is coupled with a BlockAddID that identifies the kind of data it contains. The following table defines the meanings of BlockAddID values.

BlockAddID Value	Definition
0	Invalid.
1	Indicates that the context of the `BlockAdditional` data is defined by the corresponding `Codec Mapping`.
2 or greater	`BlockAddID` values of 2 and greater are mapped to the `BlockAddIDValue` of the `BlockAdditionMapping` of the associated Track.

The values of BlockAddID that are 2 of greater have no semantic meaning, but simply associate the BlockMore Element with a BlockAdditionMapping of the associated Track. See on Block Additional Mappings for more information. The following XML depicts the nested Elements of a BlockGroup Element with an example of BlockAdditions: {Binary data of a VP9 video frame in YUV} 1 {alpha channel encoding to supplement the VP9 frame} ]]>

Citation Documentation of the associated normative and informative references for the codec is RECOMMENDED.

Deprecation Date A timestamp, expressed in that notes when support for the Codec Mapping within Matroska was deprecated. If a Codec Mapping is defined with a Deprecation Date, then it is RECOMMENDED that Matroska Writers SHOULD NOT use the Codec Mapping after the Deprecation Date.

Superseded By A Codec Mapping MAY only be defined with a Superseded By value, if it has an expressed Deprecation Date. If used, the Superseded By value MUST store the Codec ID of another Codec Mapping that has superseded the Codec Mapping.

Recommendations for the Creation of New Codec Mappings Creators of new Codec Mappings to be used in the context of Matroska:

SHOULD assume that all Codec Mappings they create might become standardized, public, commonly deployed, or usable across multiple implementations.
SHOULD employ meaningful values for Codec ID and Codec Name that they have reason to believe are currently unused.
SHOULD NOT prefix their Codec ID with "X_" or similar constructs.

These recommendations are based on .

Video Codec Mappings

V_MS/VFW/FOURCC Codec ID: V_MS/VFW/FOURCC Codec Name: Microsoft (TM) Video Codec Manager (VCM) Description: The private data contains the VCM structure BITMAPINFOHEADER including the extra private bytes, as defined by Microsoft. The data are stored in little-endian format (like on IA32 machines). Where is the Huffman table stored in HuffYUV, not AVISTREAMINFO ??? And the FourCC, not in AVISTREAMINFO.fccHandler ??? Initialization: Private Data contains the VCM structure BITMAPINFOHEADER including the extra private bytes, as defined by Microsoft in https://msdn.microsoft.com/en-us/library/windows/desktop/dd183376(v=vs.85).aspx. Citation: https://msdn.microsoft.com/en-us/library/windows/desktop/dd183376(v=vs.85).aspx

V_UNCOMPRESSED Codec ID: V_UNCOMPRESSED Codec Name: Video, raw uncompressed video frames Description: All details about the used color specs and bit depth are to be put/read from the TrackEntry\Video\UncompressedFourCC elements. Initialization: none

V_MPEG4/ISO/SP Codec ID: V_MPEG4/ISO/SP Codec Name: MPEG4 ISO simple profile (DivX4) Description: Stream was created via improved codec API (UCI) or even transmuxed from AVI (no b-frames in Simple Profile), frame order is coding order. Initialization: none

V_MPEG4/ISO/ASP Codec ID: V_MPEG4/ISO/ASP Codec Name: MPEG4 ISO advanced simple profile (DivX5, XviD, FFMPEG) Description: Stream was created via improved codec API (UCI) or transmuxed from MP4, not simply transmuxed from AVI. Note there are differences how b-frames are handled in these original streams, when being compared to a VfW created stream, as here there are no dummy frames inserted, the frame order is exactly the same as the coding order, same as in MP4 streams. Initialization: none

V_MPEG4/ISO/AP Codec ID: V_MPEG4/ISO/AP Codec Name: MPEG4 ISO advanced profile Description: Stream was created via improved codec API (UCI) or transmuxed from MP4, not simply transmuxed from AVI. Note there are differences how b-frames are handled in these original streams, when being compared to a VfW created stream, as here there are no dummy frames inserted, the frame order is exactly the same as the coding order, same as in MP4 streams. Initialization: none

V_MPEG4/MS/V3 Codec ID: V_MPEG4/MS/V3 Codec Name: Microsoft (TM) MPEG4 V3 Description: Microsoft (TM) MPEG4 V3 and derivates, means DivX3, Angelpotion, SMR, etc.; stream was created using VfW codec or transmuxed from AVI; note that V1/V2 are covered in VfW compatibility mode. Initialization: none

V_MPEG1 Codec ID: V_MPEG1 Codec Name: MPEG 1 Description: The Matroska video stream will contain a demuxed Elementary Stream (ES), where block boundaries are still to be defined. It's RECOMMENDED to use MPEG2MKV.exe for creating those files, and to compare the results with self-made implementations Initialization: none

V_MPEG2 Codec ID: V_MPEG2 Codec Name: MPEG 2 Description: The Matroska video stream will contain a demuxed Elementary Stream (ES), where block boundaries are still to be defined. It's RECOMMENDED to use MPEG2MKV.exe for creating those files, and to compare the results with self-made implementations Initialization: none

V_MPEG4/ISO/AVC Codec ID: V_MPEG4/ISO/AVC Codec Name: AVC/H.264 Description: Individual pictures (which could be a frame, a field, or 2 fields having the same timestamp) of AVC/H.264 stored as described in . Initialization: The Private Data contains a AVCDecoderConfigurationRecord structure, as defined in . For legacy reasons, because Block Addition Mappings are preferred; see , the AVCDecoderConfigurationRecord structure MAY be followed by an extension block beginning with a 4-byte extension block size field in big-endian byte order which is the size of the extension block minus 4 (excluding the size of the extension block size field) and a 4-byte field corresponding to a BlockAddIDType of "mvcC" followed by a content corresponding to the content of BlockAddIDExtraData for mvcC; see .

V_MPEGH/ISO/HEVC Codec ID: V_MPEGH/ISO/HEVC Codec Name: HEVC/H.265 Description: Individual pictures (which could be a frame, a field, or 2 fields having the same timestamp) of HEVC/H.265 stored as described in . Initialization: The Private Data contains a HEVCDecoderConfigurationRecord structure, as defined in .

V_MPEGI/ISO/VVC Codec ID: V_MPEGI/ISO/VVC Codec Name: VVC/H.266 Description: Individual pictures (which could be a frame, a field, or 2 fields having the same timestamp) of VVC/H.266 stored as described in . Initialization: The Private Data contains a VVCDecoderConfigurationRecord structure, as defined in .

V_AVS2 Codec ID: V_AVS2 Codec Name: AVS2-P2/IEEE.1857.4 Description: Individual pictures of AVS2-P2 stored as described in the second part of . Initialization: none.

V_AVS3 Codec ID: V_AVS3 Codec Name: AVS3-P2/IEEE.1857.10 Description: Individual pictures of AVS3-P2 stored as described in the second part of . Initialization: none.

V_REAL/RV10 Codec ID: V_REAL/RV10 Codec Name: RealVideo 1.0 aka RealVideo 5 Description: Individual slices from the Real container are combined into a single frame. Initialization: The Private Data contains a real_video_props_t structure in big-endian byte order as found in librmff.

V_REAL/RV20 Codec ID: V_REAL/RV20 Codec Name: RealVideo G2 and RealVideo G2+SVT Description: Individual slices from the Real container are combined into a single frame. Initialization: The Private Data contains a real_video_props_t structure in big-endian byte order as found in librmff.

V_REAL/RV30 Codec ID: V_REAL/RV30 Codec Name: RealVideo 8 Description: Individual slices from the Real container are combined into a single frame. Initialization: The Private Data contains a real_video_props_t structure in big-endian byte order as found in librmff.

V_REAL/RV40 Codec ID: V_REAL/RV40 Codec Name: rv40 : RealVideo 9 Description: Individual slices from the Real container are combined into a single frame. Initialization: The Private Data contains a real_video_props_t structure in big-endian byte order as found in librmff.

V_QUICKTIME Codec ID: V_QUICKTIME Codec Name: Video taken from QuickTime(TM) files Description: Several codecs as stored in QuickTime (e.g., Sorenson or Cinepak). Initialization: The Private Data contains all additional data that is stored in the 'stsd' (sample description) atom in the QuickTime file after the mandatory video descriptor structure (starting with the size and FourCC fields). For an explanation of the QuickTime file format read QuickTime File Format Specification.

V_THEORA Codec ID: V_THEORA Codec Name: Theora Initialization: The Private Data contains the first three Theora packets in order. The lengths of the packets precedes them. The actual layout is:

Byte 1: number of distinct packets #p minus one inside the CodecPrivate block. This MUST be "2" for current (as of 2016-07-08) Theora headers.
Bytes 2..n: lengths of the first #p packets, coded in Xiph-style lacing. The length of the last packet is the length of the CodecPrivate block minus the lengths coded in these bytes minus one.
Bytes n+1..: The Theora identification header, followed by the commend header followed by the codec setup header. Those are described in the Theora specs.

V_PRORES Codec ID: V_PRORES Codec Name: Apple ProRes Initialization: The Private Data contains the FourCC as found in MP4 movies:

ap4x: ProRes 4444 XQ
ap4h: ProRes 4444
apch: ProRes 422 High Quality
apcn: ProRes 422 Standard Definition
apcs: ProRes 422 LT
apco: ProRes 422 Proxy
aprh: ProRes RAW High Quality
aprn: ProRes RAW Standard Definition

this page for more technical details on ProRes

V_VP8 Codec ID: V_VP8 Codec Name: VP8 Codec format Description: VP8 is an open and royalty free video compression format developed by Google and created by On2 Technologies as a successor to VP7. Codec BlockAdditions: A single-channel encoding of an alpha channel MAY be stored in BlockAdditions. The BlockAddId of the BlockMore containing these data MUST be 1. Initialization: none

V_VP9 Codec ID: V_VP9 Codec Name: VP9 Codec format Description: VP9 is an open and royalty free video compression format developed by Google as a successor to VP8. Draft VP9 Bitstream and Decoding Process Specification Codec BlockAdditions: A single-channel encoding of an alpha channel MAY be stored in BlockAdditions. The BlockAddId of the BlockMore containing these data MUST be 1. Initialization: none

V_FFV1 Codec ID: V_FFV1 Codec Name: FF Video Codec 1 Description: FFV1 is a lossless intra-frame video encoding format designed to efficiently compress video data in a variety of pixel formats. Compared to uncompressed video, FFV1 offers storage compression, frame fixity, and self-description, which makes FFV1 useful as a preservation or intermediate video format. Draft FFV1 Specification Initialization: For FFV1 versions 0 or 1, Private Data SHOULD NOT be written. For FFV1 version 3 or greater, the Private Data MUST contain the FFV1 Configuration Record structure, as defined in https://tools.ietf.org/html/draft-ietf-cellar-ffv1-04#section-4.2, and no other data.

Audio Codec Mappings

A_MPEG/L3 Codec ID: A_MPEG/L3 Codec Name: MPEG Audio 1, 2, 2.5 Layer III Description: The data contain everything needed for playback in the MPEG Audio header of each frame. Corresponding ACM wFormatTag : 0x0055 Initialization: none

A_MPEG/L2 Codec ID: A_MPEG/L2 Codec Name: MPEG Audio 1, 2 Layer II Description: The data contain everything needed for playback in the MPEG Audio header of each frame. Corresponding ACM wFormatTag : 0x0050 Initialization: none

A_MPEG/L1 Codec ID: A_MPEG/L1 Codec Name: MPEG Audio 1, 2 Layer I Description: The data contain everything needed for playback in the MPEG Audio header of each frame. Corresponding ACM wFormatTag : 0x0050 Initialization: none

A_PCM/INT/BIG Codec ID: A_PCM/INT/BIG Codec Name: PCM Integer Big Endian Description: The audio bit depth MUST be read and set from the BitDepth Element. Audio samples MUST be considered as signed values, except if the audio bit depth is 8 which MUST be interpreted as unsigned values. Corresponding ACM wFormatTag : ??? Initialization: none

A_PCM/INT/LIT Codec ID: A_PCM/INT/LIT Codec Name: PCM Integer Little Endian Description: The audio bit depth MUST be read and set from the BitDepth Element. Audio samples MUST be considered as signed values, except if the audio bit depth is 8 which MUST be interpreted as unsigned values. Corresponding ACM wFormatTag : 0x0001 Initialization: none

A_PCM/FLOAT/IEEE Codec ID: A_PCM/FLOAT/IEEE Codec Name: Floating-Point, IEEE compatible Description: The audio bit depth MUST be read and set from the BitDepth Element (32 bit in most cases). The floats are stored as defined in and in little-endian order. Corresponding ACM wFormatTag : 0x0003 Initialization: none

A_MPC Codec ID: A_MPC Codec Name: MPC (musepack) SV8 Description: The main developer for musepack has requested that we wait until the SV8 framing has been fully defined for musepack before defining how to store it in Matroska.

A_AC3 Codec ID: A_AC3 Codec Name: (Dolby™) AC3 Description: BSID <= 8 !! The private data is void ??? Corresponding ACM wFormatTag : 0x2000 ; channel number have to be read from the corresponding audio element

A_AC3/BSID9 Codec ID: A_AC3/BSID9 Codec Name: (Dolby™) AC3 Description: The ac3 frame header has, similar to the mpeg-audio header a version field. Normal ac3 is defined as bitstream id 8 (5 Bits, numbers are 0-15). Everything below 8 is still compatible with all decoders that handle 8 correctly. Everything higher are additions that break decoder compatibility. For the samplerates 24kHz (00); 22,05kHz (01) and 16kHz (10) the BSID is 9 For the samplerates 12kHz (00); 11,025kHz (01) and 8kHz (10) the BSID is 10 Initialization: none

A_AC3/BSID10 Codec ID: A_AC3/BSID10 Codec Name: (Dolby™) AC3 Description: The ac3 frame header has, similar to the mpeg-audio header a version field. Normal ac3 is defined as bitstream id 8 (5 Bits, numbers are 0-15). Everything below 8 is still compatible with all decoders that handle 8 correctly. Everything higher are additions that break decoder compatibility. For the samplerates 24kHz (00); 22,05kHz (01) and 16kHz (10) the BSID is 9 For the samplerates 12kHz (00); 11,025kHz (01) and 8kHz (10) the BSID is 10 Initialization: none

A_ALAC Codec ID: A_ALAC Codec Name: ALAC (Apple Lossless Audio Codec) Initialization: The Private Data contains ALAC's magic cookie (both the codec specific configuration as well as the optional channel layout information). Its format is described in ALAC's official source code.

A_DTS Codec ID: A_DTS Codec Name: Digital Theatre System Description: Supports DTS, DTS-ES, DTS-96/26, DTS-HD High Resolution Audio and DTS-HD Master Audio. The private data is void. Corresponding ACM wFormatTag : 0x2001 Initialization: none

A_DTS/EXPRESS Codec ID: A_DTS/EXPRESS Codec Name: Digital Theatre System Express Description: DTS Express (a.k.a. LBR) audio streams. The private data is void. Corresponding ACM wFormatTag : 0x2001 Initialization: none

A_DTS/LOSSLESS Codec ID: A_DTS/LOSSLESS Codec Name: Digital Theatre System Lossless Description: DTS Lossless audio that does not have a core substream. The private data is void. Corresponding ACM wFormatTag : 0x2001 Initialization: none

A_VORBIS Codec ID: A_VORBIS Codec Name: Vorbis Initialization: The Private Data contains the first three Vorbis packet in order. The lengths of the packets precedes them. The actual layout is: - Byte 1: number of distinct packets #p minus one inside the CodecPrivate block. This MUST be "2" for current (as of 2016-07-08) Vorbis headers. - Bytes 2..n: lengths of the first #p packets, coded in Xiph-style lacing. The length of the last packet is the length of the CodecPrivate block minus the lengths coded in these bytes minus one. - Bytes n+1..: The Vorbis identification header, followed by the Vorbis comment header followed by the codec setup header.

A_FLAC Codec ID: A_FLAC Codec Name: FLAC (Free Lossless Audio Codec) Initialization: The Private Data contains all the header/metadata packets before the first data packet. These include the first header packet containing only the word fLaC as well as all metadata packets.

A_REAL/14_4 Codec ID: A_REAL/14_4 Codec Name: Real Audio 1 Initialization: The Private Data contains either the "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure (differentiated by their "version" field; big-endian byte order) as found in librmff.

A_REAL/28_8 Codec ID: A_REAL/28_8 Codec Name: Real Audio 2 Initialization: The Private Data contains either the "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure (differentiated by their "version" field; big-endian byte order) as found in librmff.

A_REAL/COOK Codec ID: A_REAL/COOK Codec Name: Real Audio Cook Codec (codename: Gecko) Initialization: The Private Data contains either the "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure (differentiated by their "version" field; big-endian byte order) as found in librmff.

A_REAL/SIPR Codec ID: A_REAL/SIPR Codec Name: Sipro Voice Codec Initialization: The Private Data contains either the "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure (differentiated by their "version" field; big-endian byte order) as found in librmff.

A_REAL/RALF Codec ID: A_REAL/RALF Codec Name: Real Audio Lossless Format Initialization: The Private Data contains either the "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure (differentiated by their "version" field; big-endian byte order) as found in librmff.

A_REAL/ATRC Codec ID: A_REAL/ATRC Codec Name: Sony Atrac3 Codec Initialization: The Private Data contains either the "real_audio_v4_props_t" or the "real_audio_v5_props_t" structure (differentiated by their "version" field; big-endian byte order) as found in librmff.

A_MS/ACM Codec ID: A_MS/ACM Codec Name: Microsoft(TM) Audio Codec Manager (ACM) Description: The data are stored in little-endian format (like on IA32 machines). Initialization: The Private Data contains the structure including the extra format information bytes. The structure is stored without packing or padding bytes. A WORD corresponds to a signed 2 octets integer, DWORD corresponds to a signed 4 octets integer. The extra format information are appended after the WAVEFORMATEX octets.

A_AAC/MPEG2/MAIN Codec ID: A_AAC/MPEG2/MAIN Codec Name: MPEG2 Main Profile Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG2/LC Codec ID: A_AAC/MPEG2/LC Codec Name: Low Complexity Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG2/LC/SBR Codec ID: A_AAC/MPEG2/LC/SBR Codec Name: Low Complexity with Spectral Band Replication Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG2/SSR Codec ID: A_AAC/MPEG2/SSR Codec Name: Scalable Sampling Rate Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG4/MAIN Codec ID: A_AAC/MPEG4/MAIN Codec Name: MPEG4 Main Profile Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG4/LC Codec ID: A_AAC/MPEG4/LC Codec Name: Low Complexity Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG4/LC/SBR Codec ID: A_AAC/MPEG4/LC/SBR Codec Name: Low Complexity with Spectral Band Replication Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG4/SSR Codec ID: A_AAC/MPEG4/SSR Codec Name: Scalable Sampling Rate Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_AAC/MPEG4/LTP Codec ID: A_AAC/MPEG4/LTP Codec Name: Long Term Prediction Description: Channel number and sample rate have to be read from the corresponding audio element. Audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied. AAC audio always uses wFormatTag 0xFF. Initialization: none

A_QUICKTIME Codec ID: A_QUICKTIME Codec Name: Audio taken from QuickTime(TM) files Description: Several codecs as stored in QuickTime (e.g., QDesign Music v1 or v2). Initialization: The Private Data contains all additional data that is stored in the 'stsd' (sample description) atom in the QuickTime file after the mandatory sound descriptor structure (starting with the size and FourCC fields). For an explanation of the QuickTime file format read QuickTime File Format Specification.

A_QUICKTIME/QDMC Codec ID: A_QUICKTIME/QDMC Codec Name: QDesign Music Description: Initialization: The Private Data contains all additional data that is stored in the 'stsd' (sample description) atom in the QuickTime file after the mandatory sound descriptor structure (starting with the size and FourCC fields). For an explanation of the QuickTime file format read QuickTime File Format Specification. Superseded By: A_QUICKTIME

A_QUICKTIME/QDM2 Codec ID: A_QUICKTIME/QDM2 Codec Name: QDesign Music v2 Description: Initialization: The Private Data contains all additional data that is stored in the 'stsd' (sample description) atom in the QuickTime file after the mandatory sound descriptor structure (starting with the size and FourCC fields). For an explanation of the QuickTime file format read QuickTime File Format Specification. Superseded By: A_QUICKTIME

A_TTA1 Codec ID: A_TTA1 Codec Name: The True Audio lossless audio compressor Description: TTA format description Each frame is kept intact, including the CRC32. The header and seektable are dropped. SamplingFrequency, Channels and BitDepth are used in the TrackEntry. wFormatTag = 0x77A1 Initialization: none

A_WAVPACK4 Codec ID: A_WAVPACK4 Codec Name: WavPack lossless audio compressor Description: The Wavpack packets consist of a stripped header followed by the frame data. For multi-track (> 2 tracks) a frame consists of many packets. For more details, check the WavPack muxing description. Codec BlockAdditions: For hybrid A_WAVPACK4 encodings (that include a lossy encoding with a supplemental correction to produce a lossless encoding), the correction part is stored in BlockAdditional. The BlockAddId of the BlockMore containing these data MUST be 1. Initialization: none

A_ATRAC/AT1 Codec ID: A_ATRAC/AT1 Codec Name: Sony ATRAC1 Codec Description: The original ATRAC codec by Sony, mainly used in MiniDisc platforms. The core technical details on ATRAC1 can be found in . An example encoder/decoder can be found at . Initialization: None

Subtitle Codec Mappings

S_TEXT/UTF8 Codec ID: S_TEXT/UTF8 Codec Name: UTF-8 Plain Text Description: Basic text subtitles. For more information see on Subtitles.

S_TEXT/SSA Codec ID: S_TEXT/SSA Codec Name: Subtitles Format Description: The [Script Info] and [V4 Styles] sections are stored in the codecprivate. Each event is stored in its own Block. For more information see on SSA/ASS.

S_TEXT/ASS Codec ID: S_TEXT/ASS Codec Name: Advanced Subtitles Format Description: The [Script Info] and [V4 Styles] sections are stored in the codecprivate. Each event is stored in its own Block. For more information see on SSA/ASS.

S_TEXT/WEBVTT Codec ID: S_TEXT/WEBVTT Codec Name: Web Video Text Tracks Format (WebVTT) Description: Advanced text subtitles. For more information see on WebVTT.

S_IMAGE/BMP Codec ID: S_IMAGE/BMP Codec Name: Bitmap Description: Basic image based subtitle format; The subtitles are stored as images, like in the DVD . The timestamp in the block header of Matroska indicates the start display time, the duration is set with the Duration element. The full data for the subtitle bitmap is stored in the Block's data section.

S_DVBSUB Codec ID: S_DVBSUB Codec Name: Digital Video Broadcasting (DVB) subtitles Description: This is the graphical subtitle format used in the Digital Video Broadcasting standard. For more information see on Digital Video Broadcasting (DVB).

S_VOBSUB Codec ID: S_VOBSUB Codec Name: VobSub subtitles Description: The same subtitle format used on DVDs . Supported is only format version 7 and newer. VobSubs consist of two files, the .idx containing information, and the .sub, containing the actual data. The .idx file is stripped of all empty lines, of all comments and of lines beginning with alt: or langidx:. The line beginning with id: SHOULD be transformed into the appropriate Matroska track language element and is discarded. All remaining lines but the ones containing timestamps and file positions are put into the CodecPrivate element. For each line containing the timestamp and file position data is read from the appropriate position in the .sub file. This data consists of a MPEG program stream which in turn contains SPU packets. The MPEG program stream data is discarded, and each SPU packet is put into one Matroska frame.

S_HDMV/PGS Codec ID: S_HDMV/PGS Codec Name: HDMV presentation graphics subtitles (PGS) Description: This is the graphical subtitle format used on Blu-rays. For more information, see on HDMV text presentation.

S_HDMV/TEXTST Codec ID: S_HDMV/TEXTST Codec Name: HDMV text subtitles Description: This is the textual subtitle format used on Blu-rays. For more information, see on HDMV graphics presentation.

S_KATE Codec ID: S_KATE Codec Name: Karaoke And Text Encapsulation Description: A subtitle format developed for ogg. The mapping for Matroska is described on the Xiph wiki. As for Theora and Vorbis, Kate headers are stored in the private data as xiph-laced packets.

S_ARIBSUB Codec ID: S_ARIBSUB Codec Name: ARIB STD-B24 subtitles Description: This is the textual subtitle format used in the ISDB/ARIB broadcasting standard. For more information see on ARIB (ISDB) subtitles.

Button Codec Mappings

B_VOBBTN Codec ID: B_VOBBTN Codec Name: VobBtn Buttons Description: Based on MPEG/VOB PCI packets. The file contains a header consisting of the string "butonDVD" followed by the width and height in pixels (16-bit integer each) and 4 reserved bytes. The rest is full PCI packets.

Block Addition Mappings Registered BlockAddIDType are:

Use BlockAddIDValue Block type identifier: 0 Block type name: Use BlockAddIDValue Description: This value indicates that the actual type is stored in BlockAddIDValue instead. This value is expected to be used when it is important to have a strong compatibility with players or derived formats not supporting BlockAdditionMapping but using BlockAdditions with an unknown BlockAddIDValue, and SHOULD NOT be used if it is possible to use another value.

Opaque data Block type identifier: 1 Block type name: Opaque data Description: the BlockAdditional data is interpreted as opaque additional data passed to the codec with the Block data. BlockAddIDValue MUST be 1.

ITU T.35 metadata Block type identifier: 4 Block type name: ITU T.35 metadata Description: the BlockAdditional data is interpreted as ITU T.35 metadata, as defined by ITU-T T.35 terminal codes. BlockAddIDValue MUST be 4.

avcE Block type identifier: 0x61766345 Block type name: Dolby Vision enhancement-layer AVC configuration Description: the BlockAddIDExtraData data is interpreted as the Dolby Vision enhancement-layer AVC configuration box as described in . This extension MUST NOT be used if Codec ID is not V_MPEG4/ISO/AVC.

dvcC Block type identifier: 0x64766343 Block type name: Dolby Vision configuration Description: the BlockAddIDExtraData data is interpreted as DOVIDecoderConfigurationRecord structure, as defined in , for Dolby Vision profiles less than and equal to 7.

dvvC Block type identifier: 0x64767643 Block type name: Dolby Vision configuration Description: the BlockAddIDExtraData data is interpreted as DOVIDecoderConfigurationRecord structure, as defined in , for Dolby Vision profiles greater than 7.

hvcE Block type identifier: 0x68766345 Block type name: Dolby Vision enhancement-layer HEVC configuration Description: the BlockAddIDExtraData data is interpreted as the Dolby Vision enhancement-layer HEVC configuration as described in . This extension MUST NOT be used if Codec ID is not V_MPEGH/ISO/HEVC.

mvcC Block type identifier: 0x6D766343 Block type name: MVC configuration Description: the BlockAddIDExtraData data is interpreted as MVCDecoderConfigurationRecord structure, as defined in . This extension MUST NOT be used if Codec ID is not V_MPEG4/ISO/AVC.

Subtitles Because Matroska is a general container format, we try to avoid specifying the formats to store in it. This type of work is really outside of the scope of a container-only format. However, because the use of subtitles in A/V containers has been so limited (with the exception of DVD) we are taking the time to specify how to store some of the more common subtitle formats in Matroska. This is being done to help facilitate their growth. Otherwise, incompatibilities could prevent the standardization and use of subtitle storage. This page is not meant to be a complete listing of all subtitle formats that will be used in Matroska, it is only meant to be a guide for the more common, current formats. It is possible that we will add future formats to this page as they are created, but it is not likely as any other new subtitle format designer would likely have their own specifications. Any specification listed here SHOULD be strictly adhered to or it SHOULD NOT use the corresponding Codec ID. Here is a list of pointers for storing subtitles in Matroska:

Any Matroska file containing only subtitles SHOULD use the extension ".mks".
As a general rule of thumb for all codecs, information that is global to an entire stream SHOULD be stored in the CodecPrivate element.
Start and stop timestamps that are used in a timestamps original storage format SHOULD be removed when being placed in Matroska as they could interfere if the file is edited afterwards. Instead, the Blocks timestamp and Duration SHOULD be used to say when the timestamp is displayed.
Because a "subtitle" stream is actually just an overlay stream, anything with a transparency layer could be use, including video.

Images Subtitles The first image format that is a goal to import into Matroska is the VobSub subtitle format. This subtitle type is generated by exporting the subtitles from a DVD . The requirement for muxing VobSub into Matroska is v7 subtitles (see first line of the .IDX file). If the version is smaller, you must remux them using the SubResync utility from VobSub 2.23 (or MPC) into v7 format. Generally any newly created subs will be in v7 format. The .IFO file will not be used at all. If there is more than one subtitle stream in the VobSub set, each stream will need to be separated into separate tracks for storage in Matroska. E.g. the VobSub file contains streams for both English and German subtitles. Then the resulting Matroska file SHOULD contain two tracks. That way the language information can be dropped and mapped to Matroska's language tags. The .IDX file is reformatted (see below) and placed in the CodecPrivate. Each .BMP will be stored in its own Block. The Timestamp with be stored in the Blocks Timestamp and the duration will be stored in the Default Duration. Here is an example .IDX file: First, lines beginning with "#" are removed. These are comments to make text file editing easier, and as this is not a text file, they aren't needed. Next remove the "langidx" and "id" lines. These are used to differentiate the subtitle streams and define the language. As the streams will be stored separately anyway, there is no need to differentiate them here. Also, the language setting will be stored in the Matroska tags, so there is no need to store it here. Finally, the "timestamp" will be used to set the Block's timestamp. Once it is set there, there is no need for it to be stored here. Also, as it may interfere if the file is edited, it SHOULD NOT be stored here. Once all of these items are removed, the data to store in the CodecPrivate SHOULD look like this: There SHOULD also be two Blocks containing one image each with the timestamps "00:00:01:101" and "00:00:08:708".

SRT Subtitles SRT is perhaps the most basic of all subtitle formats. It consists of four parts, all in text: 1. A number indicating which subtitle it is in the sequence. 2. The time that the subtitle appears on the screen, and then disappears. 3. The subtitle itself. 4. A blank line indicating the start of a new subtitle. When placing SRT in Matroska, part 3 is converted to UTF-8 (S_TEXT/UTF8) and placed in the data portion of the Block. Part 2 is used to set the timestamp of the Block, and BlockDuration element. Nothing else is used. Here is an example SRT file: 00:02:20,375 Senator, we're making our final approach into Coruscant. 2 00:02:20,476 --> 00:02:22,501 Very good, Lieutenant. ]]> In this example, the text "Senator, we're making our final approach into Coruscant." would be converted into UTF-8 and placed in the Block. The timestamp of the block would be set to "00:02:17,440". And the BlockDuration element would be set to "00:00:02,935". The same is repeated for the next subtitle. Because there are no general settings for SRT, the CodecPrivate is left blank.

SSA/ASS Subtitles SSA stands for Sub Station Alpha. It's the file format used by the popular subtitle editor, SubStation Alpha. This format is widely used by fansubbers. It allows you to do some advanced display features, like positioning, karaoke, style managements... For detailed information on SSA/ASS, see the SSA specs. It includes an SSA specs description and the advanced features added by ASS format (standing for Advanced SSA). Because SSA and ASS are so similar, they are treated the same here. Like SRT, this format is text based with a particular syntax. A file consists of 4 or 5 parts, declared ala INI file (but it's not an INI !) The first, "[Script Info]" contains some information about the subtitle file, such as it's title, who created it, type of script and a very important one: "PlayResY". Be careful of this value, everything in your script (font size, positioning) is scaled by it. Sub Station Alpha uses your desktops Y resolution to write this value, so if a friend with a large monitor and a high screen resolution gives you an edited script, you can mess everything up by saving the script in SSA with your low-cost monitor. The second, "[V4 Styles]", is a list of style definitions. A style describe how will look a text on the screen. It defines font, font size, primary/.../outile colour, position, alignment, etc. For example, this: The third, "[Events]", is the list of text you want to display at the right timing. You can specify some attribute here. Like the style to use for this event (MUSTbe defined in the list), the position of the text (Left, Right, Vertical Margin), an effect. Name is mostly used by translator to know who said this sentence. Timing is in h:mm:ss.cc (centisec). "[Pictures]" or "[Fonts]" part can be found in some SSA file, they contains UUE-encoded pictures/font but those features are only used by Sub Station Alpha -- i.e., no filter (Vobsub/Avery Lee Subtiler filter) use them. Now, how are they stored in Matroska?

All text is converted to UTF-8
All the headers are stored in CodecPrivate (Script Info and the Styles list)
Start & End field are used to set TimeStamp and the BlockDuration element. the data stored is:
Events are stored in the Block in this order: ReadOrder, Layer, Style, Name, MarginL, MarginR, MarginV, Effect, Text (Layer comes from ASS specs ... it's empty for SSA.) "ReadOrder field is needed for the decoder to be able to reorder the streamed samples as they were placed originally in the file."

Here is an example of an SSA file. Here is what would be placed into the CodecPrivate element. And here are the two blocks that would be generated. Block's timestamp: 00:02:40.650 BlockDuration: 00:00:01.140 Block's timestamp: 00:02:42.420 BlockDuration: 00:00:01.730

WebVTT The "Web Video Text Tracks Format" (short: WebVTT) is developed by the World Wide Web Consortium (W3C). Its specifications are freely available. The guiding principles for the storage of WebVTT in Matroska are:

Consistency: store data in a similar way to other subtitle codecs
Simplicity: making decoding and remuxing as easy as possible for existing infrastructures
Completeness: keeping as much data as possible from the original WebVTT file

Storage of WebVTT in Matroska

CodecID: codec identification The CodecID to use is S_TEXT/WEBVTT.

CodecPrivate: storage of global WebVTT blocks This element contains all global blocks before the first subtitle entry. This starts at the "WEBVTT" file identification marker but excludes the optional byte order mark.

Storage of non-global WebVTT blocks Non-global WebVTT blocks (e.g., "NOTE") before a WebVTT Cue Text are stored in Matroska's BlockAddition element together with the Matroska Block containing the WebVTT Cue Text these blocks precede (see below for the actual format).

Storage of Cues in Matroska blocks Each WebVTT Cue Text is stored directly in the Matroska Block. A muxer MUST change all WebVTT Cue Timestamps present within the Cue Text to be relative to the Matroska Block's timestamp. The Cue's start timestamp is used as the Matroska Block's timestamp. The difference between the Cue's end timestamp and its start timestamp is used as the Matroska Block's duration.

BlockAdditions: storing non-global WebVTT blocks, Cue Settings Lists and Cue identifiers Each Matroska Block may be accompanied by one BlockAdditions element. Its format is as follows:

The first line contains the WebVTT Cue Text's optional Cue Settings List followed by one line feed character (U+0x000a). The Cue Settings List may be empty, in which case the line consists of the line feed character only.
The second line contains the WebVTT Cue Text's optional Cue Identifier followed by one line feed character (U+0x000a). The line may be empty indicating that there was no Cue Identifier in the source file, in which case the line consists of the line feed character only.
The third and all following lines contain all WebVTT Comment Blocks that precede the current WebVTT Cue Block. These may be absent.

If there is no Matroska BlockAddition element stored together with the Matroska Block, then all three components (Cue Settings List, Cue Identifier, Cue Comments) MUST be assumed to be absent.

Examples of transformation Here's an example how a WebVTT is transformed.

Example WebVTT file Let's take the following example file: 00:00:10.000 Example entry 1: Hello world. NOTE style blocks cannot appear after the first cue. 00:00:25.000 --> 00:00:35.000 Example entry 2: Another entry. This one has multiple lines. 00:01:03.000 --> 00:01:06.500 position:90% align:right size:35% Example entry 3: That stuff to the right of the timestamps are cue \ settings. 00:03:10.000 --> 00:03:20.000 Example entry 4: Entries can even include timestamps. For example:<00:03:15.000>This becomes visible five seconds after the first part. ]]>

Example of CodecPrivate The resulting CodecPrivate element will look like this:

Storage of Cue 1 Example Cue 1: timestamp 00:00:00.000, duration 00:00:10.000, Block's content: world. ]]> BlockAddition's content starts with one empty line as there's no Cue Settings List:

Storage of Cue 2 Example Cue 2: timestamp 00:00:25.000, duration 00:00:10.000, Block's content: BlockAddition's content starts with two empty lines as there's neither a Cue Settings List nor a Cue Identifier:

Storage of Cue 3 Example Cue 3: timestamp 00:01:03.000, duration 00:00:03.500, Block's content: BlockAddition's content ends with an empty line as there's no Cue Identifier and there were no WebVTT Comment blocks:

Storage of Cue 4 Example Cue 4: timestamp 00:03:10.000, duration 00:00:10.000, Block's content: Example entry 4: Entries can even include timestamps. For example:00:00:05.000This becomes visible five seconds after the first part. This Block does not need a BlockAddition as the Cue did not contain an Identifier, nor a Settings List, and it wasn't preceded by Comment blocks.

Storage of WebVTT in Matroska vs. WebM Note: the storage of WebVTT in Matroska is not the same as the design document for storage of WebVTT in WebM. There are several reasons for this including but not limited to: the WebM document is old (from February 2012) and was based on an earlier draft of WebVTT and ignores several parts that were added to WebVTT later; WebM does still not support subtitles at all; the proposal suggests splitting the information across multiple tracks making demuxer's and remuxer's life very difficult.

HDMV presentation graphics subtitles The specifications for the HDMV presentation graphics subtitle format (short: HDMV PGS) can be found in the document "Blu-ray Disc Read-Only Format; Part 3 — Audio Visual Basic Specifications" in section 9.14 "HDMV graphics streams".

Storage of HDMV presentation graphics subtitles The CodecID to use is S_HDMV/PGS. A CodecPrivate element is not used.

Storage of HDMV PGS Segments in Matroska Blocks Each HDMV PGS Segment (short: Segment) will be stored in a Matroska Block. A Segment is the data structure described in section 9.14.2.1 "Segment coding structure and parameters" of the Blu-ray specifications. Each Segment contains a presentation timestamp. This timestamp will be used as the timestamp for the Matroska Block. A Segment is normally shown until a subsequent Segment is encountered. Therefore, the Matroska Block MAY have no Duration. In that case, a player MUST display a Segment within a Matroska Block until the next Segment is encountered. A muxer MAY use a Duration, e.g., by calculating the distance between two subsequent Segments. If a Matroska Block has a Duration, a player MUST display that Segment only for the duration of the Block's Duration.

HDMV text subtitles The specifications for the HDMV text subtitle format (short: HDMV TextST) can be found in the document "Blu-ray Disc Read-Only Format; Part 3 — Audio Visual Basic Specifications" in section 9.15 "HDMV text subtitle streams".

Storage of HDMV text subtitles The CodecID to use is S_HDMV/TEXTST. A CodecPrivate Element is required. It MUST contain the stream's Dialog Style Segment as described in section 9.15.4.2 "Dialog Style Segment" of the Blu-ray specifications.

Storage of HDMV TextST Dialog Presentation Segments in Matroska Blocks Each HDMV Dialog Presentation Segment (short: Segment) will be stored in a Matroska Block. A Segment is the data structure described in section 9.15.4.3 "Dialog presentation segment" of the Blu-ray specifications. Each Segment contains a start and an end presentation timestamp (short: start PTS & end PTS). The start PTS will be used as the timestamp for the Matroska Block. The Matroska Block MUST have a Duration, and that Duration is the difference between the end PTS and the start PTS. A player MUST use the Matroska Block's timestamp and Duration instead of the Segment's start and end PTS for determining when and how long to show the Segment.

Character set When TextST subtitles are stored inside Matroska, the only allowed character set is UTF-8. Each HDMV text subtitle stream in a Blu-ray can use one of a handful of character sets. This information is not stored in the MPEG2 Transport Stream itself but in the accompanying Clip Information file. Therefore, a muxer MUST parse the accompanying Clip Information file. If the information indicates a character set other than UTF-8, it MUST re-encode all text Dialog Presentation Segments from the indicated character set to UTF-8 prior to storing them in Matroska.

Digital Video Broadcasting (DVB) subtitles The specifications for the Digital Video Broadcasting subtitle bitstream format (short: DVB subtitles) can be found in the document "ETSI EN 300 743 - Digital Video Broadcasting (DVB); Subtitling systems". The storage of DVB subtitles in MPEG transport streams is specified in the document "ETSI EN 300 468 - Digital Video Broadcasting (DVB); Specification for Service Information (SI) in DVB systems".

Storage of DVB subtitles

CodecID The CodecID to use is S_DVBSUB.

CodecPrivate The CodecPrivate element is five bytes long and has the following structure:

2 bytes: composition page ID (bit string, left bit first)
2 bytes: ancillary page ID (bit string, left bit first)
1 byte: subtitling type (bit string, left bit first)

The semantics of these bytes are the same as the ones described in section 6.2.41 "Subtitling descriptor" of ETSI EN 300 468.

Storage of DVB subtitles in Matroska Blocks Each Matroska Block consists of one or more DVB Subtitle Segments as described in segment 7.2 "Syntax and semantics of the subtitling segment" of ETSI EN 300 743. Each Matroska Block SHOULD have a Duration indicating how long the DVB Subtitle Segments in that Block SHOULD be displayed.

ARIB (ISDB) subtitles The specifications for the ARIB B-24 subtitle bitstream format (short: ARIB subtitles) and its storage in MPEG transport streams can be found in the documents , , and .

Storage of ARIB subtitles

CodecID The CodecID to use is S_ARIBSUB.

CodecPrivate The CodecPrivate element is three bytes long and has the following structure:

1 byte: component tag (bit string, left bit first)
2 bytes: data component ID (bit string, left bit first)

The semantics of the component tag are the same as those described in , part 2, Annex J. The semantics of the data component ID are the same as those described in , fascicle 2, Vol. 3, Section 2, 4.2.8.1.

Storage of ARIB subtitles in Matroska Blocks Each Matroska Block consists of a single synchronized PES data structure as described in chapter 5 "Independent PES transmission protocol" of , volume 3, with a Synchronized_PES_data_byte block containing one or more ISDB Caption Data Groups as described in chapter 9 "Transmission of caption and superimpose" of , volume 1, part 3. All of the Caption Statement Data Groups in a given Matroska Track MUST use the same language index. A Data Group is normally shown until a subsequent Group provides instructions to clear it. Therefore, the Matroska Block SHOULD NOT have a Duration. A player SHOULD display a Data Group within a Matroska Block until its internal duration elapses, or until a subsequent Data Group removes it.

Block Additional Mapping Extra data or metadata can be added to each Block using BlockAdditional data. Each BlockAdditional contains a BlockAddID that identifies the kind of data it contains. When the BlockAddID is set to "1" the contents of the BlockAdditional Element are define by the Codec Mappings defines; see . When the BlockAddID is set a value greater than "1", then the contents of the BlockAdditional Element are defined by the BlockAdditionalMapping Element, within the associated Track Element, where the BlockAddID Element of BlockAdditional Element equals the BlockAddIDValue of the associated Track's BlockAdditionalMapping Element. That BlockAdditionalMapping Element identifies a particular Block Additional Mapping by the BlockAddIDType. The following XML depicts a use of a Block Additional Mapping to associate a timecode value with a Block: 1 568001708 1 2 timecode 12 V_FFV1

3000 {binary video frame} 2 01:00:00:00 ]]> Block Additional Mappings detail how additional data MAY be stored in the BlockMore Element with a BlockAdditionMapping Element, within the Track Element, which identifies the BlockAdditional content. Block Additional Mappings define the BlockAddIDType value reserved to identify that type of data as well as providing an optional label stored within the BlockAddIDName Element. When the Block Additional Mapping is dependent on additional contextual information, then the Mapping SHOULD describe how such additional contextual information is stored within the BlockAddIDExtraData Element. The following Block Additional Mappings are defined.

Summary of Assigned BlockAddIDType Values For convenience, the following table shows the assigned BlockAddIDType values along with the BlockAddIDName and Citation.

BlockAddIDType	BlockAddIDName	Citation
121	SMPTE ST 12-1 timecode

SMPTE ST 12-1 Timecode

Timecode Description SMPTE ST 12-1 timecode values can be stored in the BlockMore Element to associate the content of a Matroska Block with a particular timecode value. If the Block uses Lacing, the timecode value is associated with the first frame of the Lace. The Block Additional Mapping contains a full binary representation of a 64 bit SMPTE timecode value stored in big-endian format and expressed exactly as defined in Section 8 and 9 of SMPTE 12M . For convenience, here are the bit assignments for a SMPTE ST 12-1 binary representation as described in :

Bit Positions	Label
0--3	Units of frames
4--7	First binary group
8--9	Tens of frames
10	Drop frame flag
11	Color frame flag
12--15	Second binary group
16--19	Units of seconds
20--23	Third binary group
24--26	Tens of seconds
27	Polarity correction
28--31	Fourth binary group
32--35	Units of minutes
36--39	Fifth binary group
40--42	Tens of minutes
43	Binary group flag BGF0
44--47	Sixth binary group
48--51	Units of hours
52--55	Seventh binary group
56--57	Tens of hours
58	Binary group flag BGF1
59	Binary group flag BGF2
60--63	Eighth binary group

For example, a timecode value of "07:32:54;18" can be expressed as a 64 bit SMPTE 12M value as:

BlockAddIDType The BlockAddIDType value reserved for timecode is "121".

BlockAddIDName The BlockAddIDName value reserved for timecode is "SMPTE ST 12-1 timecode".

BlockAddIDExtraData BlockAddIDExtraData is unused within this block additional mapping.

Security Considerations This document inherits security considerations from the EBML and Matroska documents.

IANA Considerations To be determined.