Frequently Asked Questions

Lossless data compression is a class of data compression algorithms that allows the exact original data to be reconstructed from the compressed data. The term lossless is in contrast to lossy data compression, which only allows an approximation of the original data to be reconstructed, in exchange for better compression rates.

A lor of people think that MP3 means 'music file'. But in fact, MP3 means MPEG Audio Layer 3, and is only one way of converting music into digital files.

There are many various audio formats, and almost all of them compress the audio data so that it takes up less space on hard drive or less space on your portable music player.

Audio compression comes in two forms: lossless compression, and lossy compression.

1. LOSSY compression.
The MP3 format uses lossy compression.

This means that it loses some of the audio information found in the original to make the compressed file much smaller.
The information that lossy compression loses is the information deemed least important to the file.
In music, this tends to be the very high and very low frequencies that are not considered to add as much to the music as the range of frequencies in between.

2. LOSSLESS compression.
FLAC and many other audio formats use lossless compression.

This means that they retain every bit of information that is found in the original, so nothing is lost at all.
Because of this, lossless compression cannot make the compressed file as small as it would be using lossy compression.
However, lossless compression means that you get a smaller file without losing any information, and so is the only method that can be used when absolute fidelity is required.

Nothing. But MP3 is already being replaced by other lossy formats that claim to offer better sound quality while creating smaller files.

Creating a collection of your music in digital form, you may end up with a huge number of files in MP3 format, and then realise that nobody uses MP3 files anymore. So you'd have to start again and create all your music again in the latest format.

The advantage to creating your collection using a lossless compression format is that each file will be identical, in terms of information, to the original. The music stored in a lossless audio file will be exactly the same as the music stored on the CD (or other audio source) you created the file from.

Even though lossless audio is a perfect copy of the original, a file created with lossless compression will not be as small as a file created with lossy compression.

So if you have a limited amount of data storage on, for example, your portable music player, smaller files will mean you can fit more files on your player storage.

That is, using lossy compression may reduce the quality of the music slightly, but it allows you to take a greater number of music tracks (or albums) on the bus to work.

Lossless audio files are great for archiving your music. A while ago this would have been possible only for a small number of audio tracks, or for professionals who could afford a lot of storage devices.

However, hard drives are now so large that it is possible to store your entire CD, tape, and vinyl collections in the form of lossless audio, and still have space left to run your operating system, word processor, and games.

Because lossless audio files are an exact copy (in information - music - terms) of the original source, you can then use software that will process any of those lossless files into a lossy, smaller copy.

So if the MP3 format stops being the standard, you can just delete all your MP3s, and use software to create lossy copies of a different format, using the archive of lossless files you have built up.

Yes, of course you can convert MP3 files into any other format that you can find software for.

But because MP3s are created with lossy compression, the information they contain about the music is not a perfect copy of the original.

So you would be working from an imperfect source. Even if the format you were converting to allowed better audio quality than MP3, your converted files would not be able to make use of this extra quality, because you would be working from an MP3 file. Conversion and compression can only ever make quality stay the same or get worse; they can never make quality improve.

The only way to get more purity would be to delete all your MP3 files and start all over again, creating new files from the original audio source, be it CD or vinyl or whatever.

Keeping an archive of your music in a lossless audio format would mean that you could batch-process those lossless files to produce a collection of music files in lossy format suitable for portable players.

Using a lossless audio file is as good as using the actual source; but creating audio files automatically (using suitable software) from an entire archive of existing lossless audio files is a lot quicker than copying from the original source (e.g. ripping from CD) one source at a time.

The original lossless audio format was original digital audio format: Wave format - the WAV file.

Most people who have been using PCs for a while will have come across WAV files.
They are a lossless audio format.

In fact, typically WAV files do not even compress the data digitally, so the files are enormous. This has made them fairly useless for any serious quantity of music, until recently.

Somebody rightly points out that with hard drives being as huge as they are these days, most people could in fact store their whole music collection on a new hard drive, even using uncompressed Wave format.

But it seems a shame to use an uncompressed format when there are so many lossless compressed formats.

Even if you have got a huge hard drive, it makes sense to create the smallest files you can. Transferring files from one drive to another will take less time, for instance, if the total amount of data is smaller. And why waste drive space you don't have to?

One lossless audio format that is designed to compress the data is FLAC (Free Lossless Audio Codec). This audio format seems to have quite a lot of support, both software and hardware, and is already being used by several artitsts and music distributors as a way of offering high-fidelity music files.

Another lossless compressed format that has fans is Monkey's Audio. There seems to be no hardware support for this format, but several software applications support plug-ins that allow Monkey's Audio files to play.

Both FLAC and Monkey's Audio are open source, and free for anyone to use. Both offer a tagging or metadata, like the ID3v1 or ID3v2 tags that MP3 files offer, that store useful information about the music in each track, such as track number, track name, artist, album, year of release.

As usual, there is no answer. It's a matter of personal preference.

Using the uncompressed Wave format is quickest, but will produce bigger files.

Using FLAC will take about a quarter longer, but will reduce the size of files by about a third.

Using Monkey's Audio will take about a third longer than Wave, but will reduce the size of the files by a bit more than FLAC. It all depends on which you value more: time or space.

FLAC offers the best mix of performance and features. The difference in compression size between it and Monkey's Audio is not huge.

Even comparing FLAC's 'medium' setting to Monkey's 'extra high' setting does not produce a difference of more than a few percent. Also, FLAC is very much open source, using an OSI-approved licence, so it should remain free and available without restriction.

And FLAC seems to have been implemented in hardware devices (such as the Squeezebox, the Rio Karma, and the PhatBox) whereas Monkey's Audio has not. This could mean that you decide you don't need lossy audio formats at all, and simply keep all of your music in FLAC format.

Many lossless comparisons look at only compression ratio and speed.

FLAC decoding is the fastest among lossless codecs and it has the fastest encoding mode. FLAC's compression is within 3% of even the most complex codecs. Note that the compression ratios of all lossless codecs fall in a quite narrow range; the difference between the very best and very worst is only around 7%, and only 4% for the practical codecs.

So the evaluation of lossless codecs typically depends mainly on other features, which is what our first table shows; features like how well it is supported in devices and software, licensing, etc.

Additionally, as archiving is one of the main applications for a lossless codec, of chief importance is the ability to use and recover data in the future.

FLAC stands out as the most widely supported codec, and the only codec that at once is non-proprietary, is unencumbered by patents, has an open-source reference implementation, has a well documented format and API, and has several other independent implementations.

The rest of the tables show in detail the compression ratios and speed of the codecs in different modes. FLAC's high decoding speed is due to very low complexity and is instrumental to its support by dozens of consumer electronic devices.

Reviewed encoders (besides FLAC):

Apple Lossless - A proprietary codec by Apple.
Bonk - An open-source source codec. No player or library support yet.
La - A closed source symmetric adaptive codec. Highest compression ratio but extremely slow.
Monkey's Audio - A symmetric adaptive codec with good compression. Source is available under a non-OSI license.
Ogg Squish - An open source source codec that is no longer maintained.
optimFROG - A closed source, Windows/Linux codec, with Winamp and XMMS plugins. Slow but high compression ratios.
Shorten - A.J. Robinson's well-known codec; source is available here.
Tak - A new and efficient codec, but closed-source and Windows only.
WavPack - A fine open-source codec, released under the BSD license.

The results of comparison, technical details and conclusions you can read here.

FLAC stands for Free Lossless Audio Codec, an audio format similar to MP3, but lossless, meaning that audio is compressed in FLAC without any loss in quality. This is similar to how Zip works, except with FLAC you will get much better compression because it is designed specifically for audio, and you can play back compressed FLAC files in your favorite player (or your car or home stereo, see supported devices) just like you would an MP3 file.

FLAC stands out as the fastest and most widely supported lossless audio codec, and the only one that at once is non-proprietary, is unencumbered by patents, has an open-source reference implementation, has a well documented format and API, and has several other independent implementations.

FLAC supports tagging, cover art, and fast seeking. 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 many programs and devices that support FLAC, but the core FLAC project here maintains the format and provides programs and libraries for working with FLAC files. See Getting FLAC for instructions on downloading and installing the official FLAC tools, or Using FLAC for instructions and guides on playing FLAC files, ripping CDs to FLAC, etc.

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.

Notable features of FLAC:

• 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.
• 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.
• Hardware support: FLAC is supported by dozens of consumer electronic devices, from portable players, to home stereo equipment, to car stereo.
• Flexible metadata: FLAC's metadata system supports tags, cover art, seek tables, and cue sheets. Applications can write their own APPLICATION metadata once they register an ID. New metadata blocks can be defined and implemented in future versions of FLAC without breaking older streams or decoders.
• Seekable: FLAC supports fast sample-accurate seeking. Not only is this useful for playback, it makes FLAC files suitable for use in editing applications.
• 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.
• 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.

What FLAC is not:

• Lossy. FLAC is intended for lossless compression only, as there are many good lossy formats already, such as Vorbis, MPC, and MP3 (see LAME for an excellent open-source implementation).
• DRM. There is no intention to add any copy prevention methods. Of course, we can't stop someone from encrypting a FLAC stream in another container (e.g. the way Apple encrypts AAC in MP4 with FairPlay), that is the choice of the user.

FLAC is a general purpose audio format supported by many programs.

Most of the documentation here is about the FLAC format itself and the tools we provide, but there is also information on using other programs that support FLAC.

To download official FLAC tools go here.

And to see the extras section for other third-party tools go here.

I recommend to Windows users, use free player foobar2000 which supports MP3, MP4, AAC, CD Audio, WMA, Vorbis, FLAC, WavPack, WAV, AIFF, Musepack...

Also in foobar2000 you can convert from/to lossless/lossy formats, join and split files using cue-sheets and even rip Audio CDs.