Introduction
Apple Lossless (also known as Apple Lossless Encoder, ALE, or Apple Lossless Audio Codec, ALAC) is an audio codec developed by Apple Inc. for lossless data compression of digital music.
Apple Lossless data is stored within an MP4 container with the filename extension .m4a – this extension is also used by Apple for AAC audio data in an MP4 container (same container, different audio encoding). However, Apple Lossless is not a variant of AAC (which is a lossy format), but rather a distinct lossless format that uses linear prediction similar to other lossless codecs such as FLAC and Shorten. All current iPods and iPhones can play Apple Lossless-encoded files. It does not use any digital rights management (DRM) scheme, but by the nature of the container, it is thought that DRM could be applied to ALAC much the same way it can with other files in QuickTime containers.
Apple claims that 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, similar to other lossless formats. Furthermore, the speed at which it can be decoded makes it useful for a limited-power device such as the iPod.
The Apple Lossless Encoder was introduced into Mac OS X' Core Audio framework on April 28, 2004 together with the QuickTime 6.5.1 update, and thus available in iTunes as of version 4.5 and above. The codec is also used in the AirPort Express's AirPlay implementation.
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