Like all matter in the universe, MPEG-4 files are also made of “atoms” — it’s the term given for the set of nested data that comprises the structure of an MPEG-4 file. Atoms are key to the way the audio and video data within an MPEG-4 file are accessed. They figure in how Apple’s digital rights management (DRM) scheme is used to protect music file purchases from its iTunes Music Store. (Apple uses the AAC file format; AAC is the audio layer in MPEG-4 files.) Atoms also factor in how hymn is able to “scrub” protected AAC files of Apple’s DRM.
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