Quote Originally Posted by 3rdalbum View Post
...but AAC does support DRM...
Not exactly. The DRM implementation included in MPEG-4 (AAC is defined in MPEG-4 Part 3 - likewise, Part 2 is the video standard Xvid implements and Part 10 is H.264/AVC), known as Intellectual Property Management and Protection or IPMP, is standard-practice for the specification (in fact, the MPEG-2 spec also includes IPMP). But, that's not the DRM usually used, of which most people would be familiar with. What is typically found instead is Apple's FairPlay DRM, which has no connection to the MPEG-4 standard at all. Feasibly they could repackage MP3s or Vorbis files in the MP4 container and slap FairPlay on them too, but the likelihood of that is very very small, IMO.

Case in point: the audio ID tag for a FairPlay'ed file isn't mp4a, which it normally would be, but drms (the corresponding video ID is drmv rather than the normal mp4v, avc1, etc.). I'm not even sure if it even lies in the audio sector of the MP4 files at all, because MP4 allows for the use of private sectors (which I understand to be roughly similar to the Attachments feature of MKV, but I could be wrong).

At most the argument could be made for the MP4 container allowing for DRM (AAC is simply the audio format, much like Vorbis is the audio format and Ogg is the container), but even then the standard scheme used is third-party and could probably be done even on other MPEG standard files, if they chose to. Basically my view of it is that the standard is left somewhat open-ended, so the ability to use DRM is there, but doing it properly (according to official spec) just isn't done.