Free Lossless Audio Codec

Free Lossless Audio Codec

Developer(s)	Xiph.Org Foundation, Josh Coalson
Initial release	20 July 2001
Stable release	1.2.1 / 17 September 2007; 3 years ago (2007-09-17)
Operating system	Cross-platform
Type	Audio codec, Audio file format
License	command-line utilities: GNU GPL libraries: BSD
Website	flac.sourceforge.net

Free Lossless Audio Codec (FLAC) is an audio compression codec primarily authored by Josh Coalson and Ed Whitney. As its name implies, FLAC employs a lossless data compression algorithm: a digital audio recording compressed by FLAC can be decompressed into an identical copy of the original audio data. Audio sources encoded to FLAC are typically reduced to 50–60% of their original size.^[2]

FLAC is an open and royalty-free format with a free software implementation made available. FLAC has support for tagging, cover art, and fast seeking. Though FLAC playback support in portable audio devices and dedicated audio systems is limited compared to formats like MP3,^[3] FLAC is supported by more hardware devices than competing lossless formats like WavPack.^[4]

History

Development started in 2000 by Josh Coalson.^[5] The bit-stream format was frozen when FLAC entered beta stage with the release of version 0.5 of the reference implementation on January 15, 2001. Version 1.0 was released on 20 July 2001.^[5]

On 29 January 2003, the Xiph.Org Foundation and the FLAC project announced the incorporation of FLAC under the Xiph.org banner. Xiph.org is behind other free compression formats such as Vorbis, Theora, Speex, and others.^[5][6][7]

On 17 September 2007, the 1.2.1 version was released.

The project

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 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 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. 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.^[3]

Comparisons

FLAC is specifically designed for efficient packing of audio data, unlike general purpose lossless algorithms such as DEFLATE which is used in ZIP and gzip. While ZIP may compress a CD-quality audio file by 10–20%, FLAC achieves compression rates of 30–50% for most music, with significantly greater compression for voice recordings. By contrast, 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 decoded in a fast time, which is independent of compression level.

As a 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. FLAC being lossless means it is highly suitable for transcode e.g. to MP3, without the normally associated transcoding quality loss. 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.

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

Technical details

FLAC supports only fixed-point samples, not floating-point. This is to remove the imprecision of floating point arithmetic so as to ensure the encoder is fully lossless. It can handle any PCM bit resolution from 4 to 32 bits per sample, any sampling rate from 1 Hz to 655,350 Hz in 1 Hz increments,^[8] and any number of channels from 1 to 8.^[9] 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 a Rice parameter between 0–16. FLAC supports Replay Gain.

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

The reference implementation of FLAC compiles on many platforms, including most Unix (such as Solaris and Mac OS X) and Unix-like (including Linux, BSD), Windows, BeOS, and OS/2 operating systems. There are build systems for autoconf/automake, MSVC, Watcom C, and Xcode. There is currently no multicore support in libFLAC.

For tagging, FLAC uses the same system as Vorbis comments.^[10]

API organization

libFLAC API is organized into streams, seekable streams, and files (listed 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.

Software support

Encoding

Decoding

Ripping

Hardware support

Native

• TRAXMOD Open source, open hardware portable MMC/SD player supports 44.1 kHz/16-bit stereo FLAC playback.
• Onkyo TX-NR906 Supports 16 bit/24 bit at 44.1 kHz/48 kHz/96 kHz Mono & Stereo FLAC files through external USB with metatag display support.
• Pioneer SC-05, SC-07, SC-25, SC-27 and SC-09TX support via external USB (network support verified)
• Denon AVP-A1HDCI, AVR-4810, AVR-4310, AVR-3310, AVR-5308, AVR-4308, AVR-3808 AV Receivers^[19]
• Yamaha RX-V2065 AV Receiver
• Meridian Sooloos
• Escient^[20]
• iAudio (Cowon) - A2, A3, 6, 7, F2, O2, M3, M5, X5, U3, U5,^[21] D2, D2+, S9, J3 native support with newer firmware.
• Olive (Symphony, Musica, Opus)^[22]
• PhatBox Hard Drive based in car Digital Media Player from PhatNoise
• Rio Karma
• SanDisk Sansa Fuze, Clip (with updated firmware)^[23][24], Clip+ ^[25]
• Squeezebox and Transporter network music players from Logitech. Current products decode natively. Old v1 units transcode to PCM on the server.
• Sonos
• Meizu M6 Mini Player, M3 Music Card
• VEDIA A10, B6
• 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, T39, C260, C280, C290
• Trekstor Vibez
• T+A Music Player^[26]
• Linn Klimax DS (Digital Stream) - Digital Music Player
• Linn Akurate DS - Digital Music Player
• Linn Majik DS - Digital Music Player
• Linn Sneaky Music DS - Digital Music Player
• iriver E200, E150, E100 ^[27], E50, E30, Lplayer, SPINN.
• Networked Media Tank and WIKI
• Archos 5 Internet Tablet
• Archos Internet Media Tablets ^[28]
• Naim Audio HDX Hard Disk Player^[29]
• Samsung YP-U5^[30]
• Creative Zen X-Fi 2
• WD TV
• Samsung Galaxy S
• Samsung P3
• TVIX HD M-6500, N1 (cafe), HD M-6600A/N Plus, HD M-7000
• Nokia N900

Other platforms

• Nintendo Wii when running the Wii homebrew app MPlayerWii or MPlayer CE^[31]
• Apple TV, XBMC Media Center or Boxee
• iPod - 1st through 5.5th generation, iPod mini and 1st generation iPod nano (not the shuffle, 2nd/3rd gen nano, classic or touch), using third party Rockbox firmware
• Nearly all other Rockbox-compatible DAPs, including the iriver and Gigabeat (Toshiba) range of devices, plus the aforementioned iPods
• Sound Devices 7-Series Professional Audio Recorders with "badger" firmware update (v.2.24)^[32]
• Sony PlayStation Portable when running the homebrew LightMP3 application.^[33]
• Samsung YP-P3, YP-Q1, YP-Q2, YP-U5, YP-S5 (With upgraded firmware available from Samsung website)
• FLAC playback is possible on Mobile devices or phones based on Windows Mobile, or Symbian OS with either S60, Series 80 or Series 90 UI platforms, can run the free open source media player application OggPlay.^[34][35]. Also LCG Jukebox from Lonely Cat Games is able to play FLAC audio on Symbian S60 and Windows Mobile devices.
• Google Android devices running CM 3.9.6 and later or Bugless Beauty 0.8.6 / Bugless Beast 0.7.4 and later custom ROMs.

See also

• Comparison of audio formats
• Meridian Lossless Packing
• Monkey's Audio
• TTA
• WavPack
• Apple Lossless

References

External links

• Official Website
• Detailed FLAC format specification
• Comparison of lossless formats in terms of encoding/decoding speed and compression ratio, from the FLAC website
• Comparison of lossless formats by Hans Heiden (somewhat outdated)