Pazar 12 Tem 2009, 1:31

FLAC (Free Lossless Audio Codec) is an audio format similar to MP3, but it is a lossless encoding format, meaning that audio is compressed in FLAC without any loss in quality. Being a lossless compression format, FLAC does not remove any data from the audio stream, as lossy encoding formats such as MP3, AAC, and Vorbis do.

FLAC is unique as it is the fastest and most widely supported lossless audio codec, and the only one that at once is non-proprietary, and is not patented. When we say that FLAC is free it means more than just that it is available at no cost. It means that the specification of the format is fully open to the public to be used for any purpose (the FLAC project 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 known patent. It also means that all the source code is available under open-source licenses. It is the first truly open and free lossless audio format.

The FLAC format was first programmed Josh Coalson. FLAC has been specifically designed for efficient compression and packing of audio data, unlike general lossless algorithms such as ZIP and gzip. While ZIP may compress a CD quality audio file by 10 - 20 percent, FLAC achieves compression rates of 30 - 50 percent for most music, with significantly greater compression for voice recordings. Lossy codec formats can achieve compression ratios of 80% or more by discarding data from the original stream. The main strength of FLAC compared to other lossless codecs is its ability to be streamed and decoded instantly, whatever may be the compression level.

The European Broadcasting Union (EBU) has taken up the FLAC format for its Euroradio network for the distribution of high quality Internet audio.

Features

Lossless: The encoding of audio (PCM) data incurs no loss of information, and the decoded audio is bit-for-bit identical to what went into the encoder. Each frame contains a 16-bit CRC of the frame data for detecting transmission errors. The integrity of the audio data is further insured by storing an MD5 signature of the original unencoded audio data in the file header, which can be compared against later during decoding or testing. If the original audio data is lost or damaged, a FLAC copy of the audio tracks guarantees that an exact copy of the original data can be recovered at any time. An exact restoration from a lossy archive (like the MP3 format) of the original audio data is impossible. A FLAC file can optionally be created when ripping a CD. If a CD is read and ripped into the FLAC format, the FLAC file can later be burned into an audio CD that is a perfect replica of the original audio CS data, including track order, pregaps, and CD-Text. However, additional data present on some audio CDs such as lyrics and CD+G graphics are beyond the scope of a FLAC file and most ripping programs, and the data will not be stored.

Fast: FLAC is asymmetric in favor of decode speed. Decoding requires only integer arithmetic, and is much less compute-intensive than for most perceptual codecs. Real-time decode performance is easily achievable on even 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.

Hardware support: Because of FLAC's free reference implementation and low decoding complexity, FLAC is currently the only lossless codec that has any kind of hardware support.

Streamable: Each FLAC frame contains enough data to decode that frame. FLAC does not even rely on previous or following frames. FLAC uses sync codes and CRCs (similar to MPEG and other formats), which, along with framing, allow decoders to pick up in the middle of a stream with a minimum of delay.

Seekable: FLAC supports fast sample-accurate seeking. Not only is this useful for playback, it makes FLAC files suitable for use in editing applications.

Flexible metadata: New metadata blocks can be defined and implemented in future versions of FLAC without breaking older streams or decoders. Currently there are metadata types for tags, cue sheets, and seek tables. Applications can write their own APPLICATION metadata once they register an ID.

Suitable for archiving: FLAC is an open format, and there is no generation loss if you need to convert your data to another format in the future. In addition to the frame CRCs and MD5 signature, flac has a verify option that decodes the encoded stream in parallel with the encoding process and compares the result to the original, aborting with an error if there is a mismatch.

Convenient CD archiving: FLAC has a cue sheet metadata block for storing a CD table of contents and all track and index points. For instance, you can rip a CD to a single file, then import the CD's extracted cue sheet while encoding to yield a single file representation of the entire CD. If your original CD is damaged, the cue sheet can be exported later in order to burn an exact copy.

Error resistant: Because of FLAC's framing, stream errors limit the damage to the frame in which the error occurred, typically a small fraction of a second worth of data. Contrast this with some other lossless codecs, in which a single error destroys the remainder of the stream.

Channels: 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.

Pros

* Portable to many systems
* Source open and freely licenced
* Hardware support (PhatBox, Kenwood MusicKeg, Rio Karma, etc. See below)
* Streaming support
* Extremely fast decoding
* Supports multichannel and high resolution streams
* Supports Replay Gain
* Supports cue-sheet (with some limitations)
* Gaining wide use as successor to Shorten

Cons

* Compresses less efficiently than other popular modern compressors (Monkey's Audio, OptimFROG)
* Higher compression modes slow, for little gain over the default setting.

Software that supports:

FLAC is freely available and supported on most operating systems, including Windows, UNIX (Linux, *BSD, Solaris, OS X, IRIX), BeOS, OS/2, and Amiga. There are build systems for autotools, MSVC, Watcom C, and Project Builder.

Players
* Apollo
* Cog — for Mac OS X
* foobar2000
* JRiver Media Center
* LAMIP
* MediaMonkey
* MPlayer
* MythTV
* QCD (plugin)
* VLC
* VUPlayer
* Winamp
* Windows Media Player and other directshow-based players (MPC, TCMP, RadLight) (with Illiminable's directshow filters or CoreFLAC)
* Xine
* XMMS
* XMplay

Converters

* dBpowerAMP Music Converter / Audio Player / CD Writer
* MediaMonkey Music Manager / Audio Player / CD Writer
* GX:Transcoder Music converter

CD writers/rippers

* Ahead Nero Burning Rom
* Arson
* burnatonce
* Burrrn Audio CD burner
* Exact Audio Copy CD Ripper
* CDex CD ripper
* CD Wave
* MediaMonkey - MediaMonkey CD ripper/writer

http://farm3.static.flickr.com/2513/3711539963_d47b18bd7c.jpg

Links:

Flac: http://flac.sourceforge.net/documentation_tools_flac.html#flac_options_tag

Lossless comparison: http://wiki.hydrogenaudio.org/index.php?title=Lossless_comparison & http://www.synthetic-soul.co.uk/comparison/lossless/index.asp?Sort=Compression&Desc=0

Last.fm group: http://www.lastfm.pt/group/The+Sound+Quality

With all of the advantages of FLAC, this is a happy trade off for many audiophiles.

Thanks!

PiresMachine