FLAC (Free Lossless Audio Codec)


Jul 12 2009, 5h31

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.


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.


* 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


* 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.

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


* 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


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.




  • two2two

    Whit out any doubt, IMO the best lossless format available for music lover! Screw mp3, all the way flac =D! As we can see, the benefits out wights the contras, so why bother? I recently changed my whole music collection to flac and I must say that one can hear the the difference! Some might say that it doesn't work on your mp3 player, guess what, convert it ^^. I do like flac for home entertainment, thats for sure.

    Jul 12 2009, 5h42
  • aprisoneroflove

    I use Apple Lossless, personally and AAC for my iPod. Sounds much better than mp3.

    Jul 12 2009, 5h59
  • tronic5454

    The file sizes are killer! I'm fine with 320's, ty! Then again, my hearing isn't picky enough to tell the diff.

    Jul 12 2009, 22h04
  • Silvaer

    If iTunes adds support for FLAC then I can see myself using it, but at the moment I use Apple Lossless like Aprisoneroflove, for it's ease yet lossless formating.

    Jul 14 2009, 0h45
  • The_Mu

    For burning CDs? FLAC all the way. For my iPod? A resounding NO. Seriously, I can't tell the difference between FLAC/ALAC and 320kbps mp3 through headphones, and if you can, you have really sensitive ears/are a liar.

    Jul 14 2009, 5h52
  • Krupt0

    320 kbps MP3 FTW

    Jul 14 2009, 14h16
  • aprisoneroflove

    I'm one of those audiophiles that can tell the difference between mp3 and AAC. I just have very sensitive ears. In my opinion, AAC is more true to pitch and has smaller file sizes. It's pretty much the successor to mp3, however, mp3 has more widespread usage. 320 kbps mp3 is definitely the way to go with that format.

    Jul 14 2009, 23h35
  • hhaamu

    @other commenters: That's funny, I find 320 kbps files way too large. Yet I rip my music in flac.

    Jul 15 2009, 14h41
  • Bleaki

    Not enough differences, FLAC is for elitists.

    Jul 16 2009, 21h10
  • Runiq

    It’s not about elitism! And it’s not about hearing a difference either. It’s about disk space (at least for me). I have lots of free space on my backup HD, so ripping to FLAC is a no-brainer. When I want to listen to music on my portable player, where space is valuable, I transcode to ogg or mp3. Also, flac gives me that warm fuzzy feeling in my belly.

    Set 26 2010, 21h33
  • kokocijo

    FLAC rules, no question. Also, MP3 VBR V0 > MP3 320

    Nov 1 2010, 2h49
  • dddimitriii

    The biggest (and only) con about .flac for me personally is that my music player doesn't support it :(

    Jan 29 2011, 14h31
  • Kyzumi

    FLAC and 320 kbps mp3 is pretty much the same using an average to good speaker system. the only real use for FLAC is storing music without any loss.

    Jun 24 2011, 2h51
  • SnQfcch

    FLAC is my life!!!!

    Set 25 2011, 19h19
  • BadButNotSad

    Although nobody in this group would EVER be able to hear the difference between MP3 VBR V0 and FLAC, I love FLAC because it is great for storage and you can do all editing with it without damaging it because it remains lossless :-)

    Set 15 2013, 0h19
  • BadButNotSad

    * in a blindtest of course ;-)

    Set 15 2013, 0h22
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