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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.