Format

The FLAC format is described in great detail in RFC 9639. That document also defines the mapping of FLAC in the Ogg and Matroska (mkv) containers, provides implementation guidance and contains examples walking through all decoding steps.

The old description of the FLAC format that used to be on this page for many years served as the basis for the RFC. While it lacks detail in certain places, requiring the reader to look for details in the libFLAC source code to fully understand it, it remains a useful overview and historical reference.

Additionally, there is a set of FLAC format conformance test files available to test whether a decoder has properly implemented all features of the FLAC format.