IMHO, Apple will use a proprietary DRM. I base my opinion on this article: <A HREF="http://www.applelinks.com/articles/2003/02/20030220013554.shtml" target="_new">http://www.applelinks.com/articles/2003/02/20030220013554.shtml</A> (AAC is a subset of the MPEG-4 codec.)