The FLAC format is described in great detail inRFC 9639. That document also defines the mapping of FLAC in theOgg andMatroska (mkv) containers,provides implementation guidance and containsexamples walking through all decoding steps.
Theold 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the reader to look for details in the libFLAC source code to fully understand it, it remains a useful overview and historical reference.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 ofFLAC format conformance test files available to test whether a decoder has properly implemented all features of the FLAC format.
The old document used to be at this URL, so below is a mapping from the old anchors to the appropriate sections of the RFC. This preserves deep links to those anchors.