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ALAC | Apple Lossless Audio Codec

Apple Lossless
Filename Extension .m4a
Developed by Apple Inc.
Type of format Lossless data compression, audio file format
Contained by MPEG-4 Part 14

ALAC, abbreviated from Apple Lossless Audio Codec, also known as Apple Lossless, is as audio codec for lossless data compression of digital music developed by Apple Inc.. It was initially proprietary until late 2011 when Apple made the codec available open-source and royalty-free.


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 (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. These other lossless codecs, such as FLAC and Shorten, are not natively supported in Apple's iTunes software, either in desktop operating systems (Mac OS or Windows) or iOS devices, so users of iTunes software who want to use a lossless format which allows the addition of metadata (unlike WAV/AIFF or other PCM-type formats, where metadata is usually ignored) 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.

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