Sustainability of Digital Formats: Planning for Library of Congress Collections

Supported encodings are declared via the unique Codec ID in the Matroska Codec Mappings. For H.264 files, the information is the following:

• 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.
• The Private Data contains a AVCDecoderConfigurationRecord structure, as defined in ISO.14496-15. For legacy reasons, because Block Addition Mappings are preferred, 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.

The "source" of the Matroska specification is an XML file hosted on Matroska.org's GitHub repository (although that table has not been updated since 2018). This table is also used to generate the semantic data used in libmatroska and libmatroska2.

Specification information is published concurrently in two locations: The Matroska website and the Internet Engineering Task Force (IETF) Matroska Media Container Format Specifications datatracker. Since 2018, the in-process specification for version 4 of the Matroska Media Container Format has been published as a sequence of Internet Drafts, available at Matroska Media Container Format Specifications datatracker. An early version of the specification dated January 11, 2009 authored by Alexander Noé is available on the Matroska site but it is not clear which versions are covered in this document.

For H.264, the specification is is ISO/IEC 14496-10:2003. Information technology -- Coding of audio-visual objects -- Part 10: Advanced Video Coding. See MPEG-4_AVC for more information.