Composition
The FLAC project consists of:

The stream formats
A simple container format for the stream, also called FLAC (or Native FLAC)
libFLAC, a library of reference encoders and decoders, and a metadata interface
libFLAC++, an object-oriented wrapper around libFLAC
flac, a command-line program based on libFLAC to encode and decode FLAC streams
metaflac, a command-line metadata editor for .flac files and for applying ReplayGain
Input plugins for various music players (Winamp, XMMS, foobar2000, musikCube, and many more)
With Xiph.org incorporation, the Ogg container format, suitable for streaming (also called Ogg FLAC)The specification of the stream format can be implemented by anyone without prior permission (Xiph.org reserves the right to set the FLAC specification and certify compliance), and neither the FLAC format nor any of the implemented encoding or decoding methods are covered by any patent. The reference implementation is free software. The source code for libFLAC and libFLAC++ is available under the BSD license, and the sources for flac, metaflac, and the plugins are available under the GNU General Public License. In its stated goals, the FLAC project encourages its developers not to implement copy prevention features (DRM) or lossy compression of any kind. Design
File structure
A FLAC file consists of the magic number fLaC, metadata, and encoded audio.The encoded audio is divided into frames, which consists of a header, a data block, and a CRC16 checksum. Each frame is encoded independent of each other. A frame header begins with a sync word, used to identify the beginning of a valid frame.
While ZIP may reduce the size of a CD-quality audio file by 10–20%, FLAC is able to reduce the size of audio data by 40–50% by taking advantage of the characteristics of audio. The technical strengths of FLAC compared to other lossless formats lie in its ability to be streamed and decoded quickly, independent of compression level. Since FLAC is a lossless scheme, it is suitable as an archive format for owners of CDs and other media who wish to preserve their audio collections. If the original media are lost, damaged, or worn out, a FLAC copy of the audio tracks ensures that an exact duplicate of the original data can be recovered at any time. An exact restoration from a lossy copy (e.g., MP3) of the same data is impossible. FLAC being lossless means it is highly suitable for transcoding e.g. to MP3, without the normally associated transcoding quality loss between one lossy format and another. A CUE file can optionally be created when ripping a CD. If a CD is read and ripped perfectly to FLAC files, the CUE file allows later burning of an audio CD that is identical in audio data to the original CD, including track order and pregap, but excluding CD-Text and other additional data such as lyrics and CD+G graphics. Adoption and implementations
The reference implementation of FLAC is implemented as the libFLAC core encoder & decoder library, with the main distributable program flac being the reference implementation of the libFLAC API.