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FLAC

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For other uses, seeFLAC (disambiguation).
"Flac" redirects here. For flak anti-aircraft fire, seeAnti-aircraft warfare.

Free Lossless Audio Codec
Developer(s)Xiph.Org Foundation,Josh Coalson, Erik de Castro Lopo
Initial release20 July 2001;22 years ago(2001-07-20)
Stable release
1.4.3[1] / 23 June 2023;12 months ago(23 June 2023)
Repository
Written inC,C++
Operating systemCross-platform
TypeCodec
LicenseCommand-line tools:GNU GPL
Libraries:BSD
Websitexiph.org/flac
Free Lossless Audio Codec
Filename extension
.flac
Internet media type
audio/flac
Uniform Type Identifier (UTI)org.xiph.flac
Magic numberfLaC[2]
Type of formatLosslessaudio
Standardxiph.org/flac/format.html
Open format?Yes[3]
Free format?Yes

FLAC(/flæk/;Free Lossless Audio Codec) is anaudio coding formatforlossless compressionofdigital audio,developed by theXiph.Org Foundation,and is also the name of the free software project producing the FLAC tools, the reference software package that includes acodecimplementation. Digital audio compressed by FLAC'salgorithmcan typically be reduced to between 50 and 70 percent of its original size[4]and decompresses to an identical copy of the original audio data.

FLAC is anopen formatwithroyalty-freelicensing and areference implementationwhich isfree software.FLAC has support formetadatatagging,album coverart, and fast seeking.

History[edit]

Development was started in 2000 by Josh Coalson. Thebitstreamformat was frozen with the release of version 0.9 of the reference implementation on 31 March 2001. Version 1.0 was released on 20 July 2001.[5]

On 29 January 2003, theXiph.Org Foundationand the FLAC project announced the incorporation of FLAC under the Xiph.org banner. Xiph.org is home to other free compression formats such asVorbis,Theora,SpeexandOpus.[5][6][7]

Version 1.3.0 was released on 26 May 2013, at which point development was moved to the Xiph.org git repository.[8]

In 2019, FLAC was proposed as an IETF standard.[9]

Design[edit]

FLAC is a lossless encoding oflinear pulse-code modulationdata.[10]

File structure[edit]

A FLAC file consists of themagic numberfLaC,metadata,and encoded audio.[10]

The encoded audio is divided into frames, each of which consists of a header, a data block, and aCRC16checksum. Each frame is encoded independent of each other. A frame header begins with async word,used to identify the beginning of a valid frame. The rest of the header contains the number of samples, position of the frame, channel assignment, and optionally thesample rateandbit depth.The data block contains the audio information.[10]

Metadata in FLAC precedes the audio. Properties like thesample rateand the number of channels are always contained in the metadata. It may also contain other information, thealbum coverfor example.[10]FLAC usesVorbis commentsfor textual metadata like track title and artist name.

Encoding and decoding[edit]

The FLAC encoding algorithm consists of multiple stages. In the first stage, the input audio is split into blocks. If the audiocontains multiple channels,each channel is encoded separately as a subblock. The encoder then tries to find a good mathematical approximation of the block, either by fitting a simplepolynomial,or through generallinear predictive coding.A description of the approximation, which is only a few bytes in length, is then written. Finally, the difference between the approximation and the input, called residual, is encoded usingRice coding.In many cases, a description of the approximation and the encoded residual takes up less space than usingpulse-code modulation.[10]

The decoding process is the reverse of encoding. The compressed residual is first decoded.[11][12]The description of the mathematical approximation is then used to calculate a waveform. The result is formed by adding the residual and the calculated waveform.[13][14]As FLACcompresses losslessly,the decoded waveform is identical to the waveform before encoding.

For two-channel stereo, the encoder may choose tojoint-encodethe audio. The channels are transformed into a side channel, which is the difference between the two input channels, and a mid channel, the sum of the two input channels. In place of a mid channel, the left channel or the right channel may be encoded instead, which is sometimes more space-efficient.[15]

Even though thereference encoderuses a single block size for the whole stream,[10]FLAC allows the block size in samples to vary per block.

Compression[edit]

The amount of compression is determined by various parameters, including the order of the linear prediction model and the block size. Regardless of the amount of compression, the original data can always be reconstructed perfectly.

For user's convenience, the reference implementation defines 9 compression levels, which arepresetsof the more technical parameters to the encoding algorithm. The levels are labeled from 0 to 8, with higher numbers resulting in a higher compression ratio, at the cost of compression speed. The meaning of each compression level varies by implementation.[16][17]

FLAC is optimized for decoding speed at the expense of encoding speed. A benchmark has shown that, while there is little variation in decoding speed as compression level increases, beyond the default compression level 5, the encoding process takes up considerably more time with little space saved compared to level 5.[18]

Implementation[edit]

Alongside the format, the FLAC project also contains afree and open-sourcereference implementation of FLAC called libFLAC. libFLAC contains facilities to encode and decode FLAC data and to manipulate the metadata of FLAC files. libFLAC++, anobject-orientedwrapper around libFLAC forC++,and thecommand-line programsflacandmetaflac,are also part of the reference implementation.

The FLAC format, along with libFLAC, are not known to be covered by anypatents,and anyone is free to write their own implementations of FLAC.

Comparison to other formats[edit]

FLAC is specifically designed for efficient packing of audio data, unlike general-purpose lossless algorithms such asDEFLATE,which are used inZIPandgzip.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's being lossless means it is highly suitable fortranscodinge.g. to MP3, without the normally associatedtranscoding quality lossbetween one lossy format and another. ACUE filecan optionally be created whenrippinga 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 andpregap,but excluding additional data such as lyrics andCD+Ggraphics.[19]But depending on the burning program used,CD-Textmay be recovered from the metadata stored in the CUE sheet and burned back to a new copy on blank CD-R media.

Adoption and implementations[edit]

See also:List of hardware and software that supports FLACandComparison of video container formats § Audio coding formats support

The reference implementation of FLAC is implemented as thelibFLACcore encoder & decoder library, with the main distributable programflacbeing the reference implementation of the libFLAC API. ThiscodecAPI is also available in C++ as libFLAC++. The reference implementation of FLAC compiles on many platforms, including mostUnix(such asSolaris,BSD) andUnix-like(includingLinux),Microsoft Windows,BeOS,andOS/2operating systems. There are build-systems forautoconf/automake,MSVC,Watcom C,andXcode.There is currently nomulticoresupport in libFLAC, but utilities such asGNU paralleland various graphical frontends can be used to spin up multiple instances of the encoder.

FLAC playback support in portable audio devices and dedicated audio systems is limited compared to formats such as MP3[20]or uncompressedPCM.FLAC support is included by default inWindows 10,Android,BlackBerry 10andJolladevices.

In 2014, several aftermarket mobile electronics companies introduced multimedia solutions that include support for FLAC. These include the NEX series from Pioneer Electronics and the VX404 and NX404 from Clarion.

TheEuropean Broadcasting Union(EBU) has adopted the FLAC format for the distribution of high quality audio over its Euroradio network.[21]TheWindowsoperating systemhas supported native FLAC integration since the introduction of Windows 10.[22]TheAndroid operating systemhas supported native FLAC playback since version 3.1.[23][24]macOS High SierraandiOS11 add native FLAC playback support.[25]

Among others thePonomusic player and streaming service used the FLAC format.[26][27]Bandcampinsists on a lossless format for uploading, and has FLAC as a download option.[28]TheWikimedia Foundationsponsored a free and open-source onlineECMAScriptFLAC tool for browsers supporting the requiredHTML5features.[29]

FLAC support by different operating systems
Microsoft Windows macOS Android BlackBerry OS iOS
Codec support Yes Yes Yes Yes Yes
Container support FLAC (.flac)
Matroska(.mka,.mkv)
Ogg(.oga)[30] 		FLAC (.flac)
Core Audio Format(.caf) 		FLAC (.flac) FLAC (.flac) FLAC (.flac)
Core Audio Format(.caf)
Notes

Support introduced in Windows 10.

Windows Media Player (2022)also supports FLAC in an Ogg container for live streams (e.g.Icecastinternet radio).[31]

 Support introduced in High Sierra.

Support introduced in Android 3.1.

Android natively supports regular FLAC (.flac), but not Ogg FLAC (.oga).[32]However, support for both regular FLAC and Ogg FLAC were later added to theFiles (Google)file manager.

 Support introduced in BlackBerry OS 5.0 Support introduced in iOS 11 (but depends on hardware used).

Various other containers are supported, independently from used operating system, depending on used playback software.

See also[edit]

References[edit]

  1. ^"FLAC 1.4.3 Released With More Optimizations, Drops PowerPC-Specific Code".23 June 2023.Retrieved19 February2024.
  2. ^Coalson, Josh."FLAC – format".Xiph.Org Foundation.Retrieved4 April2013."fLaC", the FLAC stream marker in ASCII, meaning byte 0 of the stream is 0x66, followed by 0x4C 0x61 0x43
  3. ^"PlayOgg!".Free Software Foundation.17 March 2010.Retrieved1 October2013.
  4. ^"Looking at Flac Compression Ratios".Steven Pigeon. 7 February 2012.Retrieved10 May2018.
  5. ^ab"Features".Xiph.Org Foundation.Retrieved23 November2023.
  6. ^"FLAC Joins Xiph.org".Xiph.org Foundation.29 January 2003.Retrieved31 August2009.
  7. ^Plant, Emmett."FLAC Joins Xiph!".Xiph.org Foundation.Archived fromthe originalon 29 May 2008.Retrieved31 August2009.
  8. ^"FLAC – changelog".Xiph.org Foundation.Retrieved15 October2013.
  9. ^van Beurden, Martijn; Weaver, Andrew.Free Lossless Audio Codec.I-D draft-ietf-cellar-flac.Retrieved14 May2023.
  10. ^abcdefCoalson, Josh."About the FLAC Format".Retrieved13 February2022.
  11. ^"stream_decoder.c".libFLAC.Retrieved19 February2022.
  12. ^libFLAC/stream_decoder.c,line 2734.
  13. ^"lpc.c".libFLAC.Retrieved19 February2022.
  14. ^libFLAC/lpc.c,lines 813–820.
  15. ^"FLAC Format Specification".FLAC.Retrieved19 February2022.
  16. ^"CUETools FLAC encoders comparison".CUETools Wiki.Retrieved27 May2013.
  17. ^"Encoding Settings".JRiver Media Centre.Retrieved27 May2013.
  18. ^"Lossless Codec Comparison".Synthetic-soul.co.uk.Archived fromthe originalon 2 February 2009.Retrieved26 November2016.
  19. ^"FAQ".FLAC.Retrieved23 September2014.
  20. ^"Links".FLAC.Retrieved24 March2009.
  21. ^"What is the EBU Musipop system?".EBU.24 August 2021.
  22. ^"Audio snobs rejoice: Windows 10 will have system-wide FLAC support".PC World.Retrieved10 July2015.
  23. ^"Android Supported Media Formats".Android.com.4 August 2011.Retrieved27 February2012.
  24. ^"Issue 1461 – android – FLAC file support enhancement request".Google Code.Retrieved5 August2011.
  25. ^"iOS 11 brings lossless FLAC audio playback to iPhone and iPad".idownloadblog.com.9 June 2017.Retrieved26 September2017.
  26. ^"FAQ".ponomusic.com.14 March 2014.Retrieved14 March2014.
  27. ^"Home".Qobuz.com.Retrieved10 April2014.
  28. ^"How and why should I upload lossless files?".Bandcamp.Retrieved16 February2022.
  29. ^Rillke (2015)."JavaScript FLAC de- and encoder".Retrieved9 February2015.
  30. ^"MIME Types and File Extensions - XiphWiki".
  31. ^"FLAC vs Ogg FLAC".
  32. ^"The Android Platform Doesn't Fully Support OGG Container Formats (OGA) [36906426] - Visible to Public - Issue Tracker".

External links[edit]

Wikimedia Commons has media related toFree Lossless Audio Codec.
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