FLAC

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Free Lossless Audio Codec
The Free Lossless Audio Codec (FLAC) logo.
Developer: Xiph.Org Foundation
Latest release: 1.1.3 / November 27, 2006
OS: Cross-platform
Use: Audio codec Encoder
License: GPL
Website: flac.sourceforge.net

FLAC, an acronym for Free Lossless Audio Codec, is a popular file format for audio data compression. It does not remove any information from the audio stream and is suitable both for everyday playback and audio archival. The FLAC format is currently well supported by many software projects and hardware support is growing.[1] FLAC also supports Replay Gain. Josh Coalson is the primary author of FLAC.

On January 29, 2003, Xiphophorus (now called the Xiph.Org Foundation) announced the incorporation of FLAC under their banner, alongside Vorbis, Ogg, Theora, Speex, and others.

Contents

[edit] The project

The FLAC project consists of:

  • the stream format
  • 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 wrapper around libFLAC
  • flac, a command-line wrapper around libFLAC to encode and decode FLAC streams
  • metaflac, a command-line metadata editor for .flac files and for applying Replay Gain
  • 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)

"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 and 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 not to implement copy prevention features of any kind. [2]

[edit] Comparisons

FLAC is for efficient 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%, FLAC achieves compression rates of 30–50%.

Lossy codecs can achieve ratios of 80% or more by 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. The technical strengths of FLAC compared to other lossless codecs lie in its ability to be streamed and in a fast decode time, which is independent of compression level.

As with any lossless scheme, FLAC is also a popular archive format for owners of CDs and other media who wish to preserve their audio collections. If the original media is 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 archive (e.g., MP3) of the same data is impossible. 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, 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 CUE file and most ripping software, so that data will not be archived.

For the best compression, but the longest encoding time this command can be used:

flac --lax -mep -b 8192 -l 32 -r 0,16 input.wav -o output.flac

The resulting file might not play on hardware players or be streamable, but it will work on software decoders. For a fully compliant file this command should be used instead:

flac -mep -b 8192 -l 32 -r 0,8 input.wav -o output.flac

The Hydrogenaudio Wiki features a comparison of lossless codecs, including FLAC.

[edit] Technical details

FLAC supports only fixed-point samples, not floating-point. This is to eliminate any rounding errors to ensure bit-perfect reproduction. It can handle any PCM bit resolution from 4 to 32 bits per sample, any sampling rate from 1 Hz to 1,048,570 Hz in 1 Hz increments, and any number of channels from 1 to 8. Channels can be grouped in cases like stereo and 5.1 channel surround to take advantage of interchannel correlations to increase compression. FLAC uses CRC checksums for identifying corrupted frames when used in a streaming protocol, and also has a complete MD5 hash of the raw PCM audio stored in its STREAMINFO metadata header.

FLAC allows for Rice parameter between 0-16, and up to 8 channels of audio and a wide range of sampling rates up to 192 kHz, in various bits-per-sample width.

FLAC is implemented as libFLAC core encoder & decoder with the main distributable program flac being the reference program utilizing libFLAC API. This codec API is also available in the C++ as the libFLAC++.

The reference implementation of FLAC compiles on many platforms, including most Unix and Unix-like (including Linux, *BSD, Solaris, and Mac OS X), Windows, BeOS, and OS/2 operating systems. There are build systems for autoconf/automake, MSVC, Watcom C, and Project Builder.

[edit] API Organization

libFLAC API is organized into streams, seekable streams and files in the order of increasing abstraction from the base FLAC bitstream. Most FLAC applications will generally restrict themselves to encoding/decoding using libFLAC at the file level interface.

[edit] Encoder

FLAC encoder is created as follows

  1. Create an instance of the encoder using FLAC__file_encoder_new()
  2. Set various parameters of this encoder like SamplingRate, BitsPerSample, NumberofChannels, LPC order, Mid-Side stereo, Rice parameter search distance, min & max residual, BlockSize, output FileName (if no output file, use stream encoder). Function calls for each of these
  3. Initialize the FLAC encoder using FLAC__file_encoder_init()
  4. Encode the raw samples using FLAC__file_encoder_process() or FLAC__file_encoder_process_interleaver() functions for each samples read from input (either ADC or File).
  5. On finishing encoding process call FLAC__file_encoder_finish(), after which you can either destroy the encoder or redo the steps for another file following steps 1-5.
  6. On Linux with a kernel 2.6.x or higher, the system automatically creates a subdirectory in the mount point of the AudioCD, with the name FLAC, so it's not necessary to use an encoder because you can just copy and paste the *.flac tracks, and the system will automatically do it. It can be done with a console or just copying and paste with KDE, for example. Of course the FLAC libraries must be installed in the system.

[edit] Software support

[edit] CDDA Burning

[edit] Playback

[edit] Ripping

  • Windows
    • BonkEnc using the FLAC.dll API
    • CDex using the external encoder option (now lists "flac.dll" as an encoder option if flac is installed)
    • DBpowerAMP with official codec
    • Exact Audio Copy using the external encoder
    • foobar2000 using the Converter plugin and the external encoder
    • MediaMonkey
    • MP3 Stream Editor using the external encoder (single mode/album mode/full cover picture support)
    • Winamp

[edit] Hardware support

  • iPod - Video, Nano, Photo, Colour, Mini (2nd generation), using third party Rockbox firmware
  • Nearly all Rockbox-compatible DAPs, including the iRiver and Gigabeat (Toshiba) range of devices, plus the aforementioned iPods
  • Hermstedt Hifidelio
  • iAudio (Cowon) - A2 (natively, from firmware v1.59), 6, M3, M5, X5, U3, also via Rockbox firmware
  • Rio Karma
  • Squeezebox network music player (v1 recodes to PCM on the server side, v2 and up decode natively on the Squeezebox)
  • Sonos
  • Meizu M6 Miniplayer
  • Pixel Magic Systems' HD Mediabox (with firmware 1.3.4 or higher)
  • Embedded Waveplayer- Module with FLAC level 0-2 support, MIDI and serial interface
  • Teclast T29
  • Trekstor Vibez

[edit] See also

Portal:Free software
 Free software Portal

[edit] External links

v • d • e
Xiph.Org

Ogg Project
Vorbis • Theora • Writ • Tarkin • Speex • Tremor • Ghost • OggUVS • OggPCM • Xiph QuickTime Components

Other projects
FLAC • Annodex • cdparanoia • XSPF • Icecast • IceShare

Related articles
Ogg Media • CMML • Chris Montgomery


Multimedia compression formats
Video compression formats ISO/IEC MPEG-1 | MPEG-2 | MPEG-4 | MPEG-4/AVC ITU-T H.261 | H.262 | H.263 | H.264 Others AVS | Dirac | Indeo | MJPEG | RealVideo | VC-1 | Theora | VP6 | VP7 | WMV
Audio compression formats ISO/IEC MPEG MPEG-1 Layer III (MP3) | MPEG-1 Layer II | AAC | HE-AAC ITU-T G.711 | G.722 | G.722.1 | G.722.2 | G.723 | G.723.1 | G.726 | G.728 | G.729 | G.729.1 | G.729a Others AC3 | ATRAC | FLAC | iLBC | Monkey's Audio | Musepack | RealAudio | SHN | Speex | Vorbis | WavPack | WMA
Image compression formats ISO/IEC/ITU-T JPEG | JPEG 2000 | JPEG-LS | JBIG | JBIG2 -- -- Others BMP | GIF | ILBM | PCX | PNG | TGA | TIFF | WMP
Media container formats General 3GP | ASF | AVI | FLV | Matroska | MP4 | MXF | NUT | Ogg | Ogg Media | QuickTime | RealMedia Audio only AIFF | AU | WAV -- --
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