FLAC WebCodecs Registration

1. Fully qualified codec strings

The codec string is "flac".

2. EncodedAudioChunk data

EncodedAudioChunk [[internal data]] is expected to be a "FRAME" as described in [FLAC].

3. AudioDecoderConfig description

description is required, and has to be the following:

• The bytes 0x66 0x4C 0x61 0x43 ("fLaC" in ASCII)

• A metadata block (called the STREAMINFO block) as described in section 7 of [FLAC]

• Optionaly other metadata blocks, that are not used by the specification

The sampleRate and numberOfChannels members are overridden by what the decoder finds in the description.

NOTE: This corresponds to the beginning of a FLAC bitstream, before the audio frames.

4. EncodedAudioChunk type

The [[type]] for an EncodedAudioChunk containing FLAC is always "key".

NOTE: Once the initialization has succeeded, any FLAC packet can be decoded at any time without error, but this might not result in the expected audio output.

5. AudioEncoderConfig extensions

partial dictionary AudioEncoderConfig {
  FlacEncoderConfig flac;
};

flac, of type FlacEncoderConfig

Contains codec specific configuration options for the FLAC codec.

5.1. FlacEncoderConfig

dictionary FlacEncoderConfig {
  [EnforceRange] unsigned long blockSize = 0;
  [EnforceRange] unsigned long compressLevel = 5;
};

To check if an FlacEncoderConfig is valid, run these steps:

1. If blockSize is not a valid block size, which is described section 5.1 of [FLAC], return false.

2. If compressLevel is specified and not within the range of 0 (fastest, least compression) and 8 (slowest, most compression) inclusively, return false.

3. Return true.

blockSize, of type unsigned long, defaulting to 0

Configures the number of samples to use per frame, of output EncodedAudioChunks.

NOTE: Use 0 to let the encoder estimate a blocksize by default.

compressLevel, of type unsigned long, defaulting to 5

Configures the compression level to use while encoding.

6. Privacy Considerations

Please refer to the section Privacy Considerations in [WEBCODECS].

7. Security Considerations

Please refer to the section Security Considerations in [WEBCODECS].