flac The FLAC file format associated with the .flac filename extension refers to the FLAC audio encoding algorithm. FLAC is the acronym for Free Lossless Audio Codec. The algorithm is from the lossless audio compression family of formats for digital audio compression. It was developed by the Xiph.Org foundation, a non-profit organization that produces open and free to use multimedia formats, and had its initial release in 2001. Though there isn't widespread compatibility for the format as compared to similar formats such as MP3, the FLAC format enjoys some compatibility and support with in car and home stereo manufacturers as well audio playback software and portable audio devices.