Lossless

Compression is lossless when decoding the compressed data gives a result which is identical bit-by-bit to the uncompressed original.

Generic file compression formats, like ZIP or RAR, are lossless. However, trying to compress raw audio with those generally results in files which are only slightly- if at all- smaller than the originals. Lossless audio formats take advantage of knowledge about real-world audio data to provide compression ratios averaging around 50% on most music.

Lossy encoders only attempt to approximate the sound of the original waveform rather than preserving all the information present in it. Losslessly compressed audio will therefore unavoidably be larger than audio compressed with any reasonable lossy encoder. However, this disadvantage is offset by lossless files' ability to be transcoded to other lossless formats without any quality degradation.

Popular lossless formats

Apple Lossless (ALAC)
Free Lossless Audio Codec (FLAC)
Lossless Audio (LA)
Lossless Predictive Audio Compression (LPAC)
Meridian Lossless Packing (MLP)
Monkey's Audio (APE)
OptimFROG
RK Audio (RKAU)
Shorten (SHN)
TAK
TTA
WavPack
WMA lossless

Oddball Formats

There are several old lossless formats that aren't really deserving of having an article all for themselves. Reasons are: lack of widespread support, lack of features, bad efficiency and, most importantly, it seems noone is really interested in them.

Most of those would have disappeared by now, but they are being preserved for posterity at rjamorim's

Advanced Digital Audio (ADA)

Marian's a-Pac

AudioZip

Dakx WAV

Entis Lab MIO

LiteWave

Pegasus SPS

RKaudio

Split2000

Sonarc

VocPack

WavArc

WaveZip/MUSICompress

Note that currently no single format can be considered best for all applications. Rather, the best format depends on the intended use, as well as a number of other factors (such as licensing and file structure). For example, Shorten and FLAC are widely used for sharing live music because of their cross-platform support and speed. Monkey's Audio is popular among Windows users for its superior compression ratio.

Comparisons

Note the specific assumptions and limitations of each comparison; in particular, results are sensitive to the music selected'

~~http://web.inter.nl.net/users/hvdh/lossless/lossless.htm~~: Includes an interesting graph of encode/decode speeds vs. file size on the All Albums page

Lossless comparison: A comparision focusing more on codec features and less on absolute encoding efficiency. Also features a table comparing most popular codecs based on their features.

http://members.home.nl/w.speek/comparison.htm: Performance Comparison of Lossless Audio Compressors - Compares file size, encode speed, decode speed for APE, FLAC, LPAC, WavPack, Shorten (SHN), RKAU, OptimFROG, LA, WMA Lossless. Updated 5-2003

http://www.bobulous.org.uk/misc/lossless_audio_2006.html: Lossless audio formats - A comparison of the rip-and-encode speed and album file size of six different lossless formats: uncompressed Wave, FLAC, WavPack, Shorten, Monkey's Audio, and OptimFROG. First published on 22nd May 2006.

External Links

~~The Lossless Audio Blog~~ Lossless Audio News & Information Site.