AVC (H.264) WebCodecs Registration

1. Fully qualified codec strings

The codec string must begin with the prefix "avc1.", and contain 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

A VideoDecoderConfig.description may or may not be required by the AVC codec depending on the bitstream format of the AVC content to be decoded.

If the VideoDecoderConfig.description includes an AVCDecoderConfigurationRecord, as defined by [iso14496-15], section 5.3.3.1, it will be assumed that the bitstream is 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 provided, it will be assumed that the bitstream is 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 VideoEncoder [[output callback]] as the VideoDecoderConfig.description of the VideoDecoderConfig. output_config.

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.