Or Apple Lossless (.m4a), which Apple says is a lossless format. Per the Wikipedia page on Apple Lossless (aka ALAC), "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 by Apple's iTunes software (either the Mac OS or Windows versions) or by 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.[2] All current iOS devices can play ALAC–encoded files." "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.[3][4] Furthermore, compared to some other formats, it is not as difficult to decode, making it practical for a limited-power device, such as older iOS devices."