From Academic Kids

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The Free Lossless Audio Codec (FLAC) Logo.

FLAC stands for Free Lossless Audio Codec. FLAC is a popular audio compression codec that is lossless. Unlike lossy codecs such as MP3 and AAC, it does not remove any information from the audio stream and is suitable both for everyday playback and for archiving audio collections. The FLAC format is currently well supported by many software and hardware audio products.

On January 29th, 2003, Xiphophorus (now called the Xiph.Org Foundation) announced the incorporation of FLAC under their Xiph.Org banner, to go along with Ogg Vorbis, Ogg Theora, and Speex.


The project

The FLAC project consists of:

  • the stream format
  • libFLAC, a library of reference encoders and decoders, and a metadata interface
  • libFLAC++, an object wrapper around libFLAC
  • flac, a command-line wrapper around libFLAC to encode and decode .flac files
  • metaflac, a command-line metadata editor for .flac files
  • input plugins for various music players (Winamp, XMMS, foobar2000, musikCube, and many more)

"Free" means that 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 that neither the FLAC format nor any of the implemented encoding/decoding methods are covered by any patent. It also means that the reference implementation is free software: the sources for libFLAC and libFLAC++ are available under Xiph.org's BSD license and the sources for flac, metaflac, and the plugins are available under the GPL.

In its stated goals, the FLAC project encourages its developers to not implement copy prevention features of any kind.[1] (http://flac.sourceforge.net/goals.html)


FLAC is distinguished from general lossless algorithms such as ZIP and gzip in that it is specifically designed for the efficient packing of audio data; while ZIP may compress a CD-quality audio file 10–20%, FLAC achieves compression rates of 30–50%.

While lossy codecs can achieve ratios of 80% or more, they do this at the expense of discarding data from the original stream. FLAC uses linear prediction to convert the audio samples to a series of small, uncorrelated numbers (known as the residual) which are stored efficiently using Golomb-Rice coding. It also uses run-length encoding for blocks of identical samples such as silent passages. FLAC's technical strengths versus other lossless codecs lie in its ability to be streamed, as well as a fast decode time that is independent of compression level.

FLAC has become the preferred lossless format for trading live music online, though others, such as Monkey's Audio are frequently used as well. It has a smaller file size than Shorten, and it is lossless, which is important to live music traders. It has recently become a favorite trading format of non-live lossless audio traders as well.

FLAC is also a popular archive format for owners of CDs and other media who wish to preserve their valuable audio collection. If the original media is lost, damaged, or wears out over time, a FLAC copy of the audio tracks ensure that an exact duplicate of the original data can be recovered at any time, unlike a lossy archive (e.g. MP3) of the same data.

FLAC supports only fixed-point samples, not floating-point. It can handle any PCM bit resolution from 4 to 32 bits per sample. It supports any sampling rate from 1 Hz to 655.35 kHz in 1 Hz increments.

FLAC compiles on many platforms: most Unices (including Linux, *BSD, Solaris, and Mac OS X), Windows, BeOS, and OS/2. There are build systems for autoconf/automake, MSVC, Watcom C, and Project Builder.

See also

External links

de:Free Lossless Audio Codec es:FLAC fr:Free Lossless Audio Codec ja:FLAC no:FLAC pl:FLAC sv:FLAC


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