Question for formats...

MPEG-4, which usually is played/encoded as an M4V file. This may require conversion for iPod, which can be done in iTunes (this does not apply to TV Shows and Movies purchased from the iTunes Store). Some can be played as MPEG-4 movies if already formatted properly.

The iPod, Apple TV and iPhone will play back videos encoded using either the MPEG-4 or H.264 codecs. These are open-standard video formats, and not in any way proprietary to Apple, but at the same time do not represent a broad portion of the video content that is currently available outside of the iTunes Store. Further, this does not represent the video standard that is used by most video recording devices, TV recording devices, or commercial DVDs. The result is that finding video content from anywhere other than the iTunes Store that is already encoded in an Apple-ready format is going to be difficult, and much of this content will therefore need to be converted.