From CCRMA Wiki
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.
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 in size 40 to 50 percent.
Flac supports tagging, cover art and fast seeking. FLAC's free and open source royalty-free nature makes it well-supported by many software applications (such as Amarok, Rhythmbox, Audacity, Songbird, among others), but FLAC playback support in portable audio devices and dedicated audio systems may be limited. Apple's iTunes needs some tweaking in order to play FLAC files.
For more info, see http://flac.sourceforge.net/faq.html
How to convert your files to FLAC (or convert to/from different formats):
- Soundconverter: http://soundconverter.berlios.de/
- Sox (great, but FLAC support has to be installed)
- Audacity (cumbersome for batch processing)
- Audialhub (great, but company went out of business)
- Peak (OK for batch processing; but see P.S. below)
- TwistedFLAC: http://twistedwave.com/TwistedFLAC.html
- Foobar: http://www.foobar2000.org/
- Tag (OS X): http://sbooth.org/Tag/#download
- EasyTag (Linux, Windows): http://easytag.sourceforge.net/
P.S. An issue with Peak's batch processing file conversion: if your original files contain letters with accents in their names, Peak will simply skip some of these files, NOT doing the conversion and NOT telling you anything. You may want to pay attention to this if you are converting hundreds of files.