Files with the FLAC (Free Lossless Audio Codec) extension are created using a compression algorithm developed by the Xiph.org non-profit organization. FLAC is the most widespread lossless audio codec and the only one that comes with open source reference implementation and it's both non-proprietary and unpatented. The FLAC File Format enables efficient audio compression without any loss of sound quality. FLAC files are 50 - 60% smaller than the original audio files used for compression. The process can also be reverted resulting in an identical copy of the uncompressed audio file. FLAC files offer support for album cover art, metadata tagging and for fast seeking.
How to open FLAC files
The FLAC format is supported by most operating systems including Windows, Linux, Amiga, OS/2, Mac OS and BeOS.