As MPEG is not a proprietary MIME, it is difficult to fully protect and at present, there is no true DRM for that MIME. MS Media offer the only fully portable DRM solution. (Others use what is referred to as AAC and it controls the access to content but not the content itself). WM files are also about 40% smaller than MPEG.
I might be bias but, I'd look into DRM Networks they have a complete solution that is very cost effective.
