Apple Lossless, also known as Apple Lossless Audio Codec, or Apple Lossless Encoder, is
an audio coding format, and its reference audio codec implementation, developed by Apple
Inc. for lossless data compression of digital music.
After initially keeping it proprietary from its inception in 2004, in late 2011 Apple
made the codec available open source and royalty-free.
Traditionally, Apple has referred to the codec as Apple Lossless, though more recently they
have begun to use the abbreviated term ALAC when referring to the codec.
Codec Apple Lossless data is stored within an MP4
container with the filename extension .m4a.
This extension is also used by Apple for lossy AAC audio data in an MP4 container.
However, Apple Lossless is not a variant of AAC, but rather a distinct lossless format
that uses linear prediction similar to other lossless codecs.
These other lossless codecs, such as FLAC and Shorten, are not natively supported by
Apple's iTunes software or by iOS devices, so users of iTunes software who want to use
a lossless format which allows the addition of metadata have to use ALAC.
All current iDevices can play ALAC–encoded files.
ALAC also does not use any DRM scheme; but by the nature of the MP4 container, it is
thought that DRM could be applied to ALAC much the same way it can with files in other
QuickTime containers.
According to Apple, audio files compressed with its lossless codec will use up "about
half the storage space" that the uncompressed data would require.
Testers using a selection of music have found that compressed files are about 40% to 60%
the size of the originals depending on the kind of music, which is similar to other lossless
formats.
Furthermore, compared to many other formats, it is not as difficult to decode, making it
practical for a limited-power device, such as iOS devices.
Partly because of the use of an MP4 container, Apple Lossless does not contain integrated
error checking, however a byproduct of this is that it allows moderately corrupted files
to continue to be playable albeit with random noise in affected blocks, unlike other lossless
formats which will generally crash or just warn the user that the file is corrupt and
not play back.
History The software for encoding into ALAC files,
Apple Lossless Encoder, was introduced into the Mac OS X Core Audio framework on April
28, 2004 together with the QuickTime 6.5.1 update; thus making it available in iTunes
since version 4.5 and above.
The codec is also used in the AirPort and AirPlay implementation.
The Apple Lossless Encoder were released as open source software under the Apache License
version 2.0 on October 27, 2011, however an independent reverse-engineered open-source
encoder and decoder were already available before the release.
Other players David Hammerton and Cody Brocious have analyzed
and decoded this codec without any documents on the format.
On March 5, 2005, Hammerton published a simple open source decoder in the programming language
C on the basis of the reverse engineering work.
The open source library libavcodec incorporates both a decoder and an encoder for Apple Lossless
format, which means that media players based on that library are able to play Apple Lossless
files.
The library was subsequently optimized for ARM processors and included in Rockbox.
foobar2000 will also play Apple Lossless files as will JRiver Media Center and BitPerfect.
See also
Comparison of audio coding formats Free Lossless Audio Codec
Monkey's Audio TTA
WavPack Windows Media Audio 9 Lossless
References
External links Apple Lossless Audio Codec Project
Technical Features of ALAC Apple - iTunes - Import
Article showing different rates of compression for different types of music