You might want to check that. i had heard that MP4 was a new video format.
I know that the old Dish network boxes used MP2 formats. I think the new boxes use MP4.
Audio-only MP4 files generally have a .m4a extension.MP4 files with audio streams encrypted by FairPlay Digital Rights Management as sold through the iTunes Music Store use the .m4p extension.
Audio book and podcast files, which also contain metadata including chapter markers, images, and hyperlinks, can use the extension .m4a, but more commonly use the .m4b extension.
[*]MP4 files with audio and video generally use the .mp4 and .m4v extensions, occasionally .mp4v.
[*]3G mobile phones use 3GP, a simplified version of MPEG-4 Part 12 (a.k.a MPEG-4/JPEG2000 ISO Base Media file format, MPEG-4 Part 14 is a derivated standard from ISO Base file format too), with the .3gp and .3g2 extensions. These files also store non-MPEG-4 data (H.263, AMR, TX3G). The common, but non-standard use of the extensions .m4a and .m4v is due to the popularity of Apple Computer's iPod and the iTunes Store
referenced from Wikipedia.