Free Lossless Audio Codec (FLAC) is a file format for lossless audio data compression. During compression, FLAC does not lose quality from the audio stream, as lossy compression formats such as MP3, AAC, and Vorbis do. Josh Coalson is the primary author of FLAC.

FLAC reduces bandwidth and storage requirements without sacrificing the integrity of the audio source. A digital audio recording (such as a CD track) encoded to FLAC can be decompressed into an identical copy of the audio data. Audio sources encoded to FLAC are typically reduced to 50–60% of their original size.[2]

FLAC is suitable for everyday audio playback and archival, with support for tagging, cover art and fast seeking. FLAC's free and open source royalty-free nature makes it well-supported by many software applications. FLAC playback support in portable audio devices and dedicated audio systems is limited at this time compared to lossy formats like MP3.[3], but Flac is supported out of the box by more hardware devices than competing lossless formats like Wavpack.

Source : http://en.wikipedia.org/wiki/Free_Lossless_Audio_Codec

comparison
Many lossless comparisons look at only compression ratio and speed. FLAC decoding is the fastest among lossless codecs and it has the fastest encoding mode. FLAC's compression is within 3% of even the most complex codecs. Note that the compression ratios of all lossless codecs fall in a quite narrow range; the difference between the very best and very worst is only around 7%, and only 4% for the practical codecs.

So the evaluation of lossless codecs typically depends mainly on other features, which is what our first table shows; features like how well it is supported in devices and software, licensing, etc. Additionally, as archiving is one of the main applications for a lossless codec, of chief importance is the ability to use and recover data in the future. FLAC stands out as the most widely supported codec, and the only codec that at once is non-proprietary, is unencumbered by patents, has an open-source reference implementation, has a well documented format and API, and has several other independent implementations.

The rest of the tables show in detail the compression ratios and speed of the codecs in different modes. FLAC's high decoding speed is due to very low complexity and is instrumental to its support by dozens of consumer electronic devices.

(Note: this comparison leaves out some archaic or impractical codecs; see below for some other comparisons. )

Reviewed encoders (besides flac of course):

* Apple Lossless - A proprietary codec by Apple.
* Bonk - An open-source source codec. No player or library support yet.
* La - A closed source symmetric adaptive codec. Highest compression ratio but extremely slow.
* Monkey's Audio - A symmetric adaptive codec with good compression. Source is available under a non-OSI license.
* Ogg Squish - An open source source codec that is no longer maintained.
* optimFROG - A closed source, Windows/Linux codec, with Winamp and XMMS plugins. Slow but high compression ratios.
* Shorten - A.J. Robinson's well-known codec; source is available here.
* Tak - A new and efficient codec, but closed-source and Windows only.
* WavPack - A fine open-source codec, released under the BSD license.

Source : http://flac. sourceforge. net/comparison. html