AVC (H.264) WebCodecs Registration

1. Fully qualified codec strings

The codec string begins with the prefix "avc1.", with a suffix of 6 characters as described in Section 3.4 of [rfc6381].

NOTE: The common "avc3." prefix is intentionally not included. This prefix does not signal a material difference to decoder inputs, so it is omitted for simplification. For the purposes of this registration, authors should simply map "avc3." to "avc1.".

2. VideoDecoderConfig description

If the VideoDecoderConfig.description is present, it is assumed to be an AVCDecoderConfigurationRecord, as defined by [iso14496-15], section 5.3.3.1, and the bitstream is assumed to be in avc format.

NOTE: This format is commonly used in .MP4 files, where the player generally has random access to the media data.

If the VideoDecoderConfig.description is not present, the bitstream is assumed to be in annexb format.

NOTE: "annexb" format is described in greater detail by [ITU-T-REC-H.264], Annex B. This format is commonly used in live-streaming applications, where including the SPS and PPS data periodically allows users to easily start from the middle of the stream.

3. VideoEncoderConfig extensions

partial dictionary VideoEncoderConfig {
  AvcEncoderConfig avc;
};

avc, of type AvcEncoderConfig

Contains codec specific configuration options for the AVC (H.264) codec.

3.1. AvcEncoderConfig

dictionary AvcEncoderConfig {
  AvcBitstreamFormat format = "avc";
};

format, of type AvcBitstreamFormat, defaulting to "avc"

Configures the format of output EncodedVideoChunks. See AvcBitstreamFormat.

3.2. AvcBitstreamFormat

enum AvcBitstreamFormat {
  "annexb",
  "avc",
};

The AvcBitstreamFormat determines the location of AVC Sequence Parameter Set (SPS) and Picture Parameter Set (PPS) data, and mechanisms for packaging the bitstream.

SPS and PPS are described in greater detail in sections G.3.41 and G.3.55 of [ITU-T-REC-H.264].

annexb

SPS and PPS data are included periodically throughout the bitstream.

NOTE: This format is described in greater detail by [ITU-T-REC-H.264], Annex B. This format is commonly used in live-streaming applications, where including the SPS and PPS data periodically allows users to easily start from the middle of the stream.

avc

SPS and PPS data are not included in the bitstream and are instead emitted via the [[output callback]] as the VideoDecoderConfig.description of the EncodedVideoChunkMetadata.decoderConfig.

NOTE: This format is described in greater detail by [iso14496-15], section 5.3.3.1. This format is commonly used in .MP4 files, where the player generally has random access to the media data.

4. EncodedVideoChunk data

EncodedVideoChunk [[internal data]] is expected to be an access unit as defined in [ITU-T-REC-H.264] section 7.4.1.2.

NOTE: An access unit contains exactly one primary coded picture.

If the bitstream is in avc format, [[internal data]] is assumed to be in canonical format, as defined in [iso14496-15] section 5.3.2.

If the bitstream is in annexb format, [[internal data]] is assumed to be in in Annex B format, as defined in [ITU-T-REC-H.264] Annex B.

NOTE: Since [[internal data]] is inherently byte-aligned, implementations are not required to recover byte-alignment.

5. EncodedVideoChunk type

If an EncodedVideoChunk's [[type]] is key, and the bitstream is in avc format, then the EncodedVideoChunk is expected to contain a primary coded picture that is an instantaneous decoding refresh (IDR) picture.

NOTE: If the bitstream is in avc format, parameter sets necessary for decoding are included in VideoDecoderConfig.description.

If an EncodedVideoChunk's [[type]] is key, and the bitstream is in annexb format, then the EncodedVideoChunk is expected to contain both a primary coded picture that is an instantaneous decoding refresh (IDR) picture, and all parameter sets necessary to decode all video data NAL units in the EncodedVideoChunk.

6. Privacy and Security Considerations

Please refer to the Privacy Considerations and Security Considerations sections in [WEBCODECS].