The .flac file format is an open-source audio format. Unlike many audio formats (E.g MP3), the .flac format uses 'lossless' audio compression, meaning audio does not lose quality when compressed. The .flac format is similar to a .zip archive in that the original data does not change. Instead, a complex algothrithm is used to compress the data and is uncompressed before each use (when you play the audio).