Codec Mapping

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 CodecID to identify and describe the format of the encoded data in its associated Clusters. This CodecID is an identifier, uniquely defined in the Matroska Codec IDs Registry (#matroska-codec-ids-registry), that represents the encoding stored within the Track. Certain encodings 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 CodecID so that all developers supporting Matroska will use the same CodecID.

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 CodecID. Each CodecID MUST be prefixed with the string from the following table according to the associated Track 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 (“_”).

Table: Codec ID Prefix by Track Type{#CodecPrefix}

Each CodecID 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 CodecID 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:

Table: Codec ID Components{#CodecComponents}

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. If the TrackEntry contains a CodecPrivate element, its data MUST be provided to the decoder.

Codec BlockAdditions

Additional data that contextualizes or supplements a Block can be stored within the BlockAdditional element of a BlockMore element [@!RFC9559, section 5.1.3.5.2.1]. Each BlockAdditional is coupled with a BlockAddID that identifies the kind of data it contains.

A BlockAddID of 1 means the data in the BlockAdditional element are tied to the codec. This BlockAdditional data with a BlockAddID of 1 MAY be passed to the associated decoder alongside the Block content .

A codec definition MUST contain a “Codec BlockAdditions” section if the codec can use BlockAdditional data with a BlockAddID of 1.

The BlockAddID values are defined in (#block-additional-mapping).

Citation

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

Superseded By

When a Superseded By is set, the superseding CodecID value MUST be used instead of the superseded CodecID.

Files MAY exist with the superseded CodecID and MAY be supported by Matroska Players.

Recommendations for the Creation of New Codec Mappings

Creators of a new Codec Mapping to be used in the context of Matroska:

• MUST assume that all Codec Mappings they create might become standardized, public, commonly deployed, or usable across multiple implementations.

• MUST employ meaningful values for CodecID and Codec Name that are not already included in the Matroska Codec IDs Registry, and are not otherwise known or suspected to be in use, even if they are not already registered.

• MUST NOT prefix their CodecID with “X_” or similar constructs.

These recommendations are based on [@!RFC6648, section 3].

Video Codec Mappings

All codecs described in this section MUST have a TrackType ([@!RFC9559, section 5.1.4.1.3]) value of “1” for video. The track using these codecs MUST contain a Video element – i.e., EBML Path \Segment\Tracks\TrackEntry\Video.

Most video codecs contain meta information about the data they contain, like encoded width and height, chroma subsampling, etc. Whenever possible these information inside the codec SHOULD be extracted and repeated at the Matroska level with the appropriate element(s) inside the \Segment\Tracks\TrackEntry\Video and \Segment\Tracks\TrackEntry elements. These values MUST be valid for the whole Segment.

V_AV1

Codec ID: V_AV1

Codec Name: Alliance for Open Media AV1 Video codec

Description: Only one Sequence Header OBU, as defined in section 6.4 of [@!AV1], is supported per Matroska Segment. Each Block contains one Temporal Unit containing one or more OBUs. Each OBU stored in the Block MUST contain its header and its payload. The OBUs in the Block follow the Low Overhead Bitstream Format syntax. They MUST have the obu_has_size_field set to 1 except for the last OBU in the frame, for which obu_has_size_field MAY be set to 0, in which case it is assumed to fill the remainder of the frame. A SimpleBlock MUST NOT be marked as a Keyframe if it doesn’t contain a Frame OBU. A SimpleBlock MUST NOT be marked as a Keyframe if the first Frame OBU doesn’t have a frame_type of KEY_FRAME. A SimpleBlock MUST NOT be marked as a Keyframe if it doesn’t contain a Sequence Header OBU. A Block inside a BlockGroup MUST use ReferenceBlock elements if the first Frame OBU in the Block has a frame_type other than KEY_FRAME. A Block inside a BlockGroup MUST use ReferenceBlock elements if the Block doesn’t contain a Sequence Header OBU. A Block with frame_header_obu where the frame_type is INTRA_ONLY_FRAME MUST use a ReferenceBlock with a value of 0 to reference itself.

Initialization: The CodecPrivate consists of the AV1CodecConfigurationRecord described in section 2.3 of [@!AV1-ISOBMFF].

PixelWidth: MUST be max_frame_width_minus_1+1 of the Sequence Header OBU.

PixelHeight: MUST be max_frame_height_minus_1+1 of the Sequence Header OBU.

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 [@!IEEE.1857-4].

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 [@!IEEE.1857-10].

Initialization: none

V_CAVS

Codec ID: V_CAVS

Codec Name: AVS1-P2, JiZhun profile

Description: Individual pictures of AVS1-P2 stored as described in [@!IEEE.1857-3].

Initialization: none

V_DIRAC

Codec ID: V_DIRAC

Codec Name: BBC Dirac

Description: A video codec developed by the BBC [@Dirac]. The Intra-only version of Dirac, also known as Dirac Pro, resulted in SMPTE VC-2 [@SMPTE.ST2042-1]. Each Matroska frame corresponds to a Sequence as defined in [@!Dirac].

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. [@!RFC9043]

Initialization: For FFV1 versions 0 or 1, CodecPrivate SHOULD NOT be written. For FFV1 version 3 or greater, the CodecPrivate MUST contain the FFV1 Configuration Record structure, as defined in [@!RFC9043, section 4.3], and no other data.

V_JPEG2000

Codec ID: V_JPEG2000

Codec Name: JPEG 2000

Description: Each Matroska frame corresponds to a JPEG 2000 image, as defined in [@!JPEG2000].

Initialization: none

V_MJPEG

Codec ID: V_MJPEG

Codec Name: Motion JPEG

Description: Motion JPEG is a video compression format in which each video frame or interlaced field is compressed separately as a [@!JPEG] image.

Initialization: none

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 [@!ISO.14496-15].

Initialization: The CodecPrivate contains a HEVCDecoderConfigurationRecord structure, as defined in [@!ISO.14496-15].

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 [@!ISO.14496-15].

Initialization: The CodecPrivate contains a VVCDecoderConfigurationRecord structure, as defined in [@!ISO.14496-15].

V_MPEG1

Codec ID: V_MPEG1

Codec Name: MPEG 1

Description: Frames correspond to a Video Sequence as defined in [@!ISO.11172-2].

Initialization: none

V_MPEG2

Codec ID: V_MPEG2

Codec Name: MPEG 2

Description: Frames correspond to a Video Sequence as defined in [@!ITU-T.H.262].

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 [@!ISO.14496-15].

Initialization: The CodecPrivate contains an AVCDecoderConfigurationRecord structure, as defined in [@!ISO.14496-15]. For legacy reasons, because Block Additional Mappings are preferred; see (#block-additional-mapping), 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 (#mvcc).

V_MPEG4/ISO/AP

Codec ID: V_MPEG4/ISO/AP

Codec Name: MPEG4 ISO Advanced Profile

Description: Frames correspond to frames defined in [@!ISO.14496-2]. 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.

Initialization: none

V_MPEG4/ISO/ASP

Codec ID: V_MPEG4/ISO/ASP

Codec Name: MPEG4 ISO Advanced Simple Profile (DivX5, XviD)

Description: Frames correspond to frames defined in [@!ISO.14496-2]. 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.

Initialization: none

V_MPEG4/ISO/SP

Codec ID: V_MPEG4/ISO/SP

Codec Name: MPEG4 ISO Simple Profile (DivX4)

Description: Frames correspond to frames defined in [@!ISO.14496-2]. Stream was created via improved codec API (UCI) or even transmuxed from AVI (no b-frames in Simple Profile).

Initialization: none

V_MPEG4/MS/V3

Codec ID: V_MPEG4/MS/V3

Codec Name: Microsoft MPEG4 V3

Description: Microsoft MPEG4 V3 and derivatives, means DivX3, Angelpotion, SMR, etc.; stream was created using VfW codec or transmuxed from AVI; note that V1/V2 are covered by the “V_MS/VFW/FOURCC” CodecID (#v-ms-vfw-fourcc).

Initialization: none

V_MS/VFW/FOURCC

Codec ID: V_MS/VFW/FOURCC

Codec Name: Microsoft Video Codec Manager (VCM)

Description: Video frames originating from Video For Windows, using the Microsoft Video Codec Manager codecs. This is a codec designed to be transmuxed back and forth from AVI sources.

Initialization: The CodecPrivate contains the VCM structure BITMAPINFOHEADER including the extra private bytes, as defined in [@!BITMAPINFOHEADER]. The data are stored in little-endian format (like on IA32 machines).

V_QUICKTIME

Codec ID: V_QUICKTIME

Codec Name: Video taken from QuickTime files

Description: Several codecs as stored in QuickTime (e.g., Sorenson or Cinepak).

Initialization: The CodecPrivate 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 [@!QTFF].

V_PRORES

Codec ID: V_PRORES

Codec Name: Apple ProRes

Initialization: The CodecPrivate 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

ProRes is defined as [@!SMPTE.RDD36].

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 CodecPrivate 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 CodecPrivate 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 CodecPrivate 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 CodecPrivate contains a real_video_props_t structure in big-endian byte order as found in [@!librmff].

V_THEORA

Codec ID: V_THEORA

Codec Name: Theora

Description: Frames correspond to a Theora Frame as defined in [@!Theora].

Initialization: The CodecPrivate 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].

V_UNCOMPRESSED

Codec ID: V_UNCOMPRESSED

Codec Name: Video, raw uncompressed video frames

Description: The codec doesn’t use any form of compression. All the relevant fields of the TrackEntry\Video element MUST be filled to play this content correctly. In addition the packing of RGB, YUV, etc. pixels MUST be declared with a TrackEntry\Video\UncompressedFourCC element with values defined in [@!RFC9559, section 5.1.4.1.28.15].

Initialization: none

V_VC1

Codec ID: V_VC1

Codec Name: VC-1

Description: Frames correspond to VC-1 samples as defined in [@!SMPTE.RP2025-2007].

Initialization: The CodecPrivate contains a VC1DecSpecStruc structure, as defined in [@!SMPTE.RP2025-2007].

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. [@?RFC6386]

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. [@!VP9]

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: Encoders are strongly encouraged to provide a CodecPrivate that contains a list of specific VP9 codec features as described in the “VP9 Codec Feature Metadata” section of [@!WebMContainer]. This piece of data helps to select a decoder on playback, but as many muxers don’t provide the CodecPrivate for “V_VP9” it is not a hard requirement. It is possible for the decoder to reconstruct the “VP9 Codec Feature Metadata” from the first frame in case the CodecPrivate is not present.

Note that the format differs from the VPCodecConfigurationRecord structure, as defined in [@VP-ISOBMFF].

Audio Codec Mappings

All codecs described in this section MUST have a TrackType ([@!RFC9559, section 5.1.4.1.3]) value of “2” for audio. The track using these codecs MUST contain an Audio element – i.e., EBML Path \Segment\Tracks\TrackEntry\Audio.

Most audio codecs contain meta information about the data they contain, like encoded sampling frequency, channel count, etc. Whenever possible these information inside the codec SHOULD be extracted and repeated at the Matroska level with the appropriate element(s) inside the \Segment\Tracks\TrackEntry\Audio and \Segment\Tracks\TrackEntry elements. These values MUST be valid for the whole Segment.

A_AAC

Codec ID: A_AAC

Codec Name: Advanced Audio Coding (AAC)

Description: Individual frames of AAC raw_data_block(), stored as defined in subpart 4 of [@!ISO.14496-3].

Initialization: The CodecPrivate contains an AudioSpecificConfig structure, as defined in [@!ISO.14496-3].

A_AAC/MPEG2/LC

Codec ID: A_AAC/MPEG2/LC

Codec Name: Low Complexity

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG2/LC/SBR

Codec ID: A_AAC/MPEG2/LC/SBR

Codec Name: Low Complexity with Spectral Band Replication

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG2/MAIN

Codec ID: A_AAC/MPEG2/MAIN

Codec Name: MPEG2 Main Profile

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG2/SSR

Codec ID: A_AAC/MPEG2/SSR

Codec Name: Scalable Sampling Rate

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG4/LC

Codec ID: A_AAC/MPEG4/LC

Codec Name: Low Complexity

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG4/LC/SBR

Codec ID: A_AAC/MPEG4/LC/SBR

Codec Name: Low Complexity with Spectral Band Replication

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG4/LTP

Codec ID: A_AAC/MPEG4/LTP

Codec Name: Long Term Prediction

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG4/MAIN

Codec ID: A_AAC/MPEG4/MAIN

Codec Name: MPEG4 Main Profile

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AAC/MPEG4/SSR

Codec ID: A_AAC/MPEG4/SSR

Codec Name: Scalable Sampling Rate

Description: The audio stream is stripped from ADTS headers and normal Matroska frame based muxing scheme is applied.

Initialization: none

Superseded By: A_AAC ((#a-aac))

A_AC3

Codec ID: A_AC3

Codec Name: Dolby Digital / AC-3

Description: Individual frames of AC-3 syncframe() stored as described in [@!ATSC.A52] or [@!ETSI.TS102-366] when the value of the bsid field defined in Section 5.4.2.1 of [@!ATSC.A52] or Section 4.4.2.1 of [@!ETSI.TS102-366] is 10 or below. Channel number have to be read from the corresponding audio element

Initialization: none

A_AC3/BSID9

Codec ID: A_AC3/BSID9

Codec Name: Dolby Digital / AC-3

Description: Individual frames of AC-3 syncframe() stored as described in [@!ATSC.A52] or [@!ETSI.TS102-366] when the value of the bsid field defined in Section 5.4.2.1 of [@!ATSC.A52] or Section 4.4.2.1 of [@!ETSI.TS102-366] is 9. Note that the value 9 in the bsid field is not standard but it is defacto used for dividing the sampling rate defined in Section 5.4.1.3 of [@!ATSC.A52] or Section 4.4.2.1 of [@!ETSI.TS102-366] by 2.

Using this Codec ID is NOT RECOMMENDED as many Matroska Players don’t support it. The generic A_AC3 Codec ID SHOULD be used instead as it supports a bsid of 9 as well.

Initialization: none

A_AC3/BSID10

Codec ID: A_AC3/BSID10

Codec Name: Dolby Digital / AC-3

Description: Individual frames of AC-3 syncframe() stored as described in [@!ATSC.A52] or [@!ETSI.TS102-366] when the value of the bsid field defined in Section 5.4.2.1 of [@!ATSC.A52] or Section 4.4.2.1 of [@!ETSI.TS102-366] is 10. Note that the value 10 in the bsid field is not standard but it is defacto used for dividing the sampling rate defined in Section 5.4.1.3 of [@!ATSC.A52] or Section 4.4.2.1 of [@!ETSI.TS102-366] by 4.

Using this Codec ID is NOT RECOMMENDED as many Matroska Players don’t support it. The generic A_AC3 Codec ID SHOULD be used instead as it supports a bsid of 10 as well.

Initialization: none

A_ALAC

Codec ID: A_ALAC

Codec Name: ALAC (Apple Lossless Audio Codec)

Initialization: The CodecPrivate contains ALAC’s magic cookie (both the codec specific configuration as well as the optional channel layout information). Its format is described in the “Magic Cookie” defined in [@!ALAC].

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 [@?AtracAES]. An example encoder/decoder can be found at [@?atracdenc].

Initialization: None

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. It corresponds to the base codec defined in [@!ETSI.TS102-114].

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. It corresponds to the LBR extension of the DTS codec defined in section 9 of [@!ETSI.TS102-114].

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. It corresponds to the Lossless extension (XLL) of the DTS codec defined in section 8 of [@!ETSI.TS102-114].

Initialization: none

A_EAC3

Codec ID: A_EAC3

Codec Name: Dolby Digital Plus / E-AC-3

Description: Individual frames of E-AC-3 syncframe() stored as described in [@!ATSC.A52] or [@!ETSI.TS102-366] when the value of the bsid field defined in Annex E Section 2.1 of [@!ATSC.A52] or Section E.1.3.1.6 of [@!ETSI.TS102-366] is 11, 12, 13, 14, 15 or 16.

Initialization: none

A_FLAC

Codec ID: A_FLAC

Codec Name: FLAC (Free Lossless Audio Codec)

Description: The mapping of the FLAC framing and CodecPrivate is described in [@!RFC9639, section 10.2].

Initialization: All FLAC data before the first audio frame; see [@!RFC9639, section 10.2].

A_MLP

Codec ID: A_MLP

Codec Name: Meridian Lossless Packing / MLP

Description: A lossless audio codec used in DVD-Audio discs. The format is similar to Dolby TrueHD ((#a-truehd)) but with fewer channels.

Initialization: none

A_MPEG/L1

Codec ID: A_MPEG/L1

Codec Name: MPEG Audio 1, 2 Layer I

Description: Frames correspond to Audio Frames of a Layer I bitstream as defined in [@!ISO.11172-3].

Initialization: none

A_MPEG/L2

Codec ID: A_MPEG/L2

Codec Name: MPEG Audio 1, 2 Layer II

Description: Frames correspond to Audio Frames of a Layer II bitstream as defined in [@!ISO.11172-3].

Initialization: none

A_MPEG/L3

Codec ID: A_MPEG/L3

Codec Name: MPEG Audio 1, 2, 2.5 Layer III

Description: Frames correspond to Audio Frames of a Layer III bitstream as defined in [@!ISO.11172-3].

Initialization: none

A_MS/ACM

Codec ID: A_MS/ACM

Codec Name: Microsoft Audio Codec Manager (ACM)

Description: The data are stored in little-endian format (like on IA32 machines).

Initialization: The CodecPrivate contains the [@!WAVEFORMATEX] 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_REAL/14_4

Codec ID: A_REAL/14_4

Codec Name: Real Audio 1

Initialization: The CodecPrivate 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 CodecPrivate 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 CodecPrivate 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 CodecPrivate 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 CodecPrivate 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 CodecPrivate 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_OPUS

Codec ID: A_OPUS

Codec Name: Opus interactive speech and audio codec

Description: The OPUS audio codec defined by [@!RFC6716] using a similar encapsulation as the Ogg Encapsulation [@!RFC7845].

Initialization: The track CodecPrivate MUST be present and contain the Identification Header defined in [@!RFC7845, section 5.1].

Channels: The track Channels element value MUST be the “Output Channel Count” value of the Identification Header.

SamplingFrequency: The track SamplingFrequency element value MUST be the “Input Sample Rate” value of the Identification Header.

CodecDelay: The track CodecDelay element MUST be present and set to the “Pre-skip” value of the Identification Header translated to Matroska Ticks. The “Pre-skip” value is in samples at 48,000 Hz. The formula to get the CodecDelay is:

CodecDelay = pre-skip * 1,000,000,000 / 48,000.

SeekPreRoll: The track SeekPreRoll element SHOULD be present and set to 80,000,000 – 80 ms in Matroska Ticks – in order to ensure that the output audio is correct by the time it reaches the seek target.

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 bits in most cases). The floats are stored as defined in [@!IEEE.754] and in little-endian order. Although [@!IEEE.754] supports “Not a Number” (“NaN”) values, if these values are present, the player behavior is unspecified and unpredictable.

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, unless the audio bit depth is 8 which MUST be interpreted as unsigned values.

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, unless the audio bit depth is 8 which MUST be interpreted as unsigned values.

Initialization: none

A_QUICKTIME

Codec ID: A_QUICKTIME

Codec Name: Audio taken from QuickTime files

Description: Several codecs as stored in QuickTime (e.g., QDesign Music v1 or v2).

Initialization: The CodecPrivate 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 [@!QTFF].

A_QUICKTIME/QDMC

Codec ID: A_QUICKTIME/QDMC

Codec Name: QDesign Music

Description:

Initialization: The CodecPrivate 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 [@!QTFF].

Superseded By: A_QUICKTIME ((#a-quicktime))

A_QUICKTIME/QDM2

Codec ID: A_QUICKTIME/QDM2

Codec Name: QDesign Music v2

Description:

Initialization: The CodecPrivate 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 [@!QTFF].

Superseded By: A_QUICKTIME ((#a-quicktime))

A_TRUEHD

Codec ID: A_TRUEHD

Codec Name: Dolby TrueHD

Description: Lossless audio codec from Dolby. Each Matroska frame corresponds to a single Access Unit as defined in [@!TRUEHD].

Initialization: none

A_TTA1

Codec ID: A_TTA1

Codec Name: The True Audio lossless audio compressor

Description: The format is described in [@!TTA]. Each frame is kept intact, including the CRC32. The header and seektable are dropped. SamplingFrequency, Channels and BitDepth are used in the TrackEntry.

Initialization: The CodecPrivate contains the TTA Header Structure, as defined in [@!TTA].

A_VORBIS

Codec ID: A_VORBIS

Codec Name: Vorbis

Initialization: The CodecPrivate 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 “Identification Header” as defined in Section 4.2.2 of [@!VORBIS], followed by the “Comment Header” as defined in Section 5 of [@!VORBIS], followed by the “Setup Header” as defined in Section 4.2.4 of [@!VORBIS].

A_WAVPACK4

Codec ID: A_WAVPACK4

Codec Name: WavPack lossless audio compressor

Description: The WavPack packets consist of a block defined in [@!WAVPACK] with a WavpackHeader header. For multichannel (> 2 channels) a frame consists of many packets. For more details, check the WavPack muxing description (#wavpack).

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: The CodecPrivate contains the version 16-bit integer from the WavpackHeader of [@!WAVPACK] stored in little-endian.

Subtitle Codec Mappings

All codecs described in this section MUST have a TrackType ([@!RFC9559, section 5.1.4.1.3]) value of “17” for subtitles.

Subtitle codecs often contain meta information about the data they contain, like expected output dimension, language, etc. Whenever possible these information inside the codec SHOULD be extracted and repeated at the Matroska level with the appropriate element(s) inside the \Segment\Tracks\TrackEntry\Video and \Segment\Tracks\TrackEntry elements. These values MUST be valid for the whole Segment.

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 (#arib-isdb-subtitles) on ARIB (ISDB) subtitles.

Initialization: The CodecPrivate data are defined in (#track-parameters-4).

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 (#digital-video-broadcasting-dvb-subtitles) on Digital Video Broadcasting (DVB).

Initialization: The CodecPrivate data are defined in (#track-parameters-3).

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 (#hdmv-text-subtitles) on HDMV text presentation.

Initialization: none

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 (#hdmv-presentation-graphics-subtitles) on HDMV graphics presentation.

Initialization: The CodecPrivate data are defined in (#track-parameters-2).

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 “Matroska mapping” section of [@!OggKate].

The codec MAY use embedded fonts from attachments, as defined in [@?RFC9559, section 21.2], in that case the TrackEntry MUST contain an AttachmentLink element.

Initialization: Kate headers are stored in the CodecPrivate as xiph-laced packets. The length of the last packet isn’t encoded, it is deduced from the sizes of the other packets and the total size of the CodecPrivate.

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 [@?DVD-Video]. The timestamp in the block header of Matroska indicates the start display time, the duration is set with the BlockDuration element. The full data for the subtitle bitmap is stored in the Block’s data section.

Initialization: none

S_TEXT/ASS

Codec ID: S_TEXT/ASS

Codec Name: Advanced SubStation Alpha Format

Description: Each event is stored in its own Block. For more information see (#ssa-ass-subtitles) on SSA/ASS.

This codec ID MUST be used when “ScriptType: v4.00+” or “[V4+ Styles]” sections are found in the original SSA script.

The codec MAY use embedded fonts from attachments, as defined in [@?RFC9559, section 21.2], in that case the TrackEntry MUST contain an AttachmentLink element.

The codec MAY also be found with the Codec ID S_ASS in legacy media containers, but using that value is NOT RECOMMENDED.

Initialization: The “[Script Info]” and “[V4 Styles]” sections are stored in the CodecPrivate.

S_TEXT/ASCII

Codec ID: S_TEXT/ASCII

Codec Name: ASCII Plain Text

Description: Basic text subtitles with only ASCII characters allowed.

Initialization: none

S_TEXT/SSA

Codec ID: S_TEXT/SSA

Codec Name: SubStation Alpha Format

Description: Each event is stored in its own Block. For more information see (#ssa-ass-subtitles) on SSA/ASS.

This codec ID MUST NOT be used when “ScriptType: v4.00+” or “[V4+ Styles]” sections are found in the original SSA script.

The codec MAY use embedded fonts from attachments, as defined in [@?RFC9559, section 21.2], in that case the TrackEntry MUST contain an AttachmentLink element.

The codec MAY also be found with the Codec ID S_SSA, but using that value is NOT RECOMMENDED.

Initialization: The “[Script Info]” and “[V4+ Styles]” sections are stored in the CodecPrivate.

S_TEXT/USF

Codec ID: S_TEXT/USF

Codec Name: Universal Subtitle Format

Description: An XML based subtitle format. Each BlockGroup contains XML data from a “subtitle” XML element as defined in section 3.4 of [@!USF], without the “subtitle” element itself and with the start, stop duration mapped to the BlockGroup timestamp and BlockDuration element. The “image” XML elements are turned into Matroska attachments and replaced in the stream with their attachment filename.

The codec MAY use embedded fonts from attachments, as defined in [@?RFC9559, section 21.2], in that case the TrackEntry MUST contain an AttachmentLink element.

Initialization: The CodecPrivate element MAY be present. If present it MAY contain “metadata”, “styles” and “effects” XML elements usable in the whole stream inside a parent “USFSubtitles” XML parent element, similar to the “USFSubtitles” element of a standalone USF file but without the “subtitles” XML element.

S_TEXT/UTF8

Codec ID: S_TEXT/UTF8

Codec Name: UTF-8 Plain Text

Description: Basic text subtitles. For more information see (#subtitle-codecs) on Subtitles.

Initialization: none

S_TEXT/WEBVTT

Codec ID: S_TEXT/WEBVTT

Codec Name: Web Video Text Tracks Format (WebVTT)

Description: Advanced text subtitles defined by [@!WebVTT]. For more information see (#webvtt).

Initialization: The CodecPrivate contains the WebVTT file body up to the first WebVTT cue block.

Codec BlockAdditions: Intermediate non-Cue Blocks SHOULD be stored in BlockAdditions. The BlockAddID of the BlockMore containing these data MUST be 1.

S_VOBSUB

Codec ID: S_VOBSUB

Codec Name: VobSub subtitles

Description: Uses data from [@!VobSub] files. The data represent subtitle data used on DVDs [@?DVD-Video]. VobSubs consist of two files, the .idx containing information, and the .sub, containing the actual data. Only version 7 and newer of VobSubs files are supported.

The line of the .idx file beginning with “id:” MUST be transformed into the appropriate Matroska track language element.

For each line of the .idx file containing a “timestamp:” and “filepos:” 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.

Initialization: The CodecPrivate contains the “palette:” and “size:” lines from the .idx file. Other lines from the .idx file not containing empty lines, comments, or starting with “alt:”; “langidx:”, “id:”, or “timestamp:” MAY be added in the CodecPrivate data for preservation.

Button Codec Mappings

All codecs described in this section MUST have a TrackType ([@!RFC9559, section 5.1.4.1.3]) value of “18” for buttons.

B_VOBBTN

Codec ID: B_VOBBTN

Codec Name: VobBtn Buttons

Description: Based on MPEG/VOB PCI packets. The frame contains a header consisting of the string “butonDVD” followed by the width and height in pixels (16-bit unsigned integer each) and 4 reserved bytes. The rest is a full PCI packet described in [@!DVD-Info.PCI].

Audio Codecs

WavPack

WavPack is an audio codec primarily designed for lossless audio, but it can also be used as a lossy codec.

[@!WAVPACK] stores each data in variable length frames. That means each frame can have a different number of samples.

Each WavPack block starts with a WavpackHeader header as defined in [@!WAVPACK], stored in little-endian.

To save space and avoid redundant information in Matroska some data from the WavpackHeader header are removed, when saved in Matroska. All the data from the WavpackHeader are kept in little-endian.

The CodecPrivate contains the version 16-bit integer from the WavpackHeader of [@!WAVPACK] stored in little-endian.

Depending on the number of audio channels and whether the hybrid mode is kept or not, the storage of WavPack blocks in Matroska differ.

Lossless And Lossy Storage

For multichannel files (more than 2 channels, like for 5.1), a frame consists of multiple WavPack blocks. The first one having the INITIAL_BLOCK (bit 11) flag set and the last one the FINAL_BLOCK (bit 12) flag set. For a mono or stereo file, both flags are set in each WavPack block.

Mono/Stereo

A Block or SimpleBlock frame contains the following header with the some fields taken from the WavpackHeader of a single WavPack block followed by the data of that WavPack block.

{
  uint32_t block_samples; // # samples in this block
  uint32_t flags;         // various flags for id and decoding
  uint32_t crc;           // crc for actual decoded data
}
[ block data ]

Multichannel

For multichannel files, a WavPack file uses multiple WavPack block to store all channels of a frame. The WavPack blocks for each channels of a frame are stored consecutively into a Matroska Block or SimpleBlock.

Each WavPack block is preceded by a header. The header for the first WavPack block is similar to the mono/stereo one ((#mono-stereo)) with the addition of a “blocksize” field, which is the size of the first WavPack block minus the WavpackHeader size. The header for the following WavPack blocks use the “flags” and “crc” of the WavpackHeader of each respective WavPack block, followed with the size of each respective WavPack block minus the WavpackHeader size.

{
  uint32_t block_samples; // # samples in this block
  uint32_t flags;         // various flags for id and decoding
  uint32_t crc;           // crc for actual decoded data
  uint32_t blocksize;     // size of the data to follow
}
[ block data # 1 ]
{
  uint32_t flags;         // various flags for id and decoding
  uint32_t crc;           // crc for actual decoded data
  uint32_t blocksize;     // size of the data to follow
}
[ block data # 2 ]
{
  uint32_t flags;         // various flags for id and decoding
  uint32_t crc;           // crc for actual decoded data
  uint32_t blocksize;     // size of the data to follow
}
[ block data # 3 ]
...

Hybrid Storage

WavPack has a hybrid mode that splits the audio frames between lossy and correction packets. Adding both gives a lossless version of the original audio. It is possible to only store the lossy part in Matroska or both together. Storing only the lossy part is equivalent to the format described in (#lossless-and-lossy-storage). This section explains how to store all hybrid data in Matroska.

Hybrid WavPack is encoded in 2 files. The first one has a lossy part and the second file has the correction part to reconstruct the original audio losslessly.

Each WavPack block in the correction file corresponds to a WavPack block in the lossy file with the same number of samples, that’s also true for a multichannel file. This means that if a frame is made of 4 WavPack blocks, the correction file will have 4 WavPack blocks in the corresponding frame. The header of the correction WavPack block is exactly the same as in the lossy WavPack block, except for the CRC.

In Matroska, the correction part is stored as an additional data available to the Block (see (#block-additional-mapping)). This way a file could be remuxed and not keep the Block Additional data and still be usable as a lossy WavPack file. The Block data of the lossy file are stored exactly the same as for lossy storage defined in (#lossless-and-lossy-storage).

A BlockAdditionMapping MUST be used for hybrid WavPack TrackEntry’.

The BlockAddIDType of that BlockAdditionMapping MUST be set to 1 for hybrid WavPack, corresponding to Opaque data; see (#opaque-data).

Each WavPack frame is stored in a BlockGroup that MUST have at least a BlockMore to hold the correction data.

The BlockAddID of that BlockMore MUST be 1, i.e., the default value.

Mono/Stereo

The BlockAdditional element of the correction data BlockMore contains the following header with the “crc” field from the WavpackHeader of the WavPack block of the correction file matching the WavPack block of the lossy frame used to fill the Block data, followed by the data of that correction file WavPack block.

{
  uint32_t crc;           // crc for actual decoded data
}
[ correction block data ]

Multichannel

The BlockAdditional element of the correction data BlockMore contains the following header with the data from the each WavpackHeader of the WavPack block of the correction file matching the WavPack block in the lossy file used to fill the Block data, followed by the data of the correction file WavPack block.

{
  uint32_t crc;           // crc for actual decoded data
  uint32_t blocksize;     // size of the data to follow
}
[ correction block data # 1 ]
{
  uint32_t crc;           // crc for actual decoded data
  uint32_t blocksize;     // size of the data to follow
}
[ correction block data # 2 ]
{
  uint32_t crc;           // crc for actual decoded data
  uint32_t blocksize;     // size of the data to follow
}
[ correction block data # 3 ]
...