From
http://www.dvdtoappletv.org/These are the specifications to watch videos in Apple TV
Apple TV
Video formats supported: H.264 and protected H.264 (from iTunes Store): 640 by 480, 30 fps, LC version of Baseline Profile; 320 by 240, 30 fps, Baseline profile up to Level 1.3; 1280 by 720, 24 fps, Progressive Main Profile. MPEG-4: 640 by 480, 30 fps, Simple Profile.
If you are converting your files with other settings Itunes isn't able to process them, so you cannot edit them (Get info)
You should not use the MPG4 option you should use H.264 option or edit the preferences for the MPG4 encoding so they match 640 by 480, 30 fps