FLAC is now formally specified in RFC 9639

19 Dec 2024

RFC 9639 has been published, specifying the Free Lossless Audio Codec (FLAC) format.

Although FLAC has had a specification document since 2000 and a open-source reference implementation filling in the details, this document should formally specify the format, such that implementers don’t have to look at the reference source code or browse the mailing list archives for details.

This publication doesn’t change the FLAC format except explicitly adding support for 32-bit audio and adding restrictions to accommodate, see here for details.

The main benefit this publications brings is that it should make writing a new FLAC decoder implementation from scratch much easier. It also provides assurance for archives wanting to use the FLAC format that their files remain decodable in the far future, in case FLAC ever becomes obsolete and its implementations unusable.

Many thanks for all who participated in improving this document.

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