FLAC stands for Free Lossless Audio Codec, a leading compression technique that preserves original audio quality while reducing file size. FLAC is an open-source, royalty-free format that has been adopted widely for its many advantages in digital audio reproduction.

Compression techniques take large files such as wave (.wav) files and reduce the data bits while preserving as much of the audio landscape as possible. A well-known audio compression format is MP3 (.mp3). MP3 files slim down bulky wave and compact disk (.cda) files to a fraction of their original size, making MP3 an ideal format for portable audio players. The MP3 format allows a vast library of songs to fill a very small storage footprint. However, there is a trade-off in audio quality.

FLAC surpasses MP3 quality by preserving the original soundscape in exact detail. The FLAC format reduces the original file size by roughly 30-60% with no loss of quality, hence it is a lossless format. This differs from the MP3 format which is a lossy format, or a format that loses quality in the conversion process.

One of the great strengths of FLAC is its very fast decoding time, or ability to stream even on modest hardware. Technical specifics in the framed architecture also allow it to be error resistant, in that each frame has the information it needs to decode itself. If a frame is corrupted, the data lost in the stream is a mere blip. This differs from other types of lossless formats where the entire stream would essentially become corrupted.

Another feature of FLAC is that it can handle up to eight channels of audio for preserving surround sound recordings. FLAC is also a good choice for archiving audio CDs, as one can always use the FLAC file later to convert to future formats. A further advantage of FLAC is that it supports replaygain, a technique for ensuring that recorded sound files play at the same volume level.

The only real disadvantage of FLAC files is that the compression ratio is not as steep as other codecs. Files will be somewhat larger. However, with all of the advantages of FLAC, this is a happy trade off for many audiophiles.

Considering the falling prices of flash cards, portable players, and storage devices, the FLAC format will likely only gain support. FLAC files can play on iPods® with installation of the open source firmware replacement, Rockbox (though this might affect warranty). FLAC files can also be played on other portable devices and on home or auto compact disc players that support the FLAC format.