I only have an iPod 4th Gen, but according to my aquaintances, it's no different from their iPad. The codec support and procedures are identical. With that said:
You need to transcode everything before uploading it through iTunes. In a nutshell, iOS is designed to be a media consumption device that doesn't actually accept most media formats.
I have a rather large collection of videos and soundtracks of various containers and codecs. And aside from MP3's, NONE OF THEM WORKS!!! Not even the h264 MP4's. Absolutely everything (aside from MP3's), has to be re-encoded to the iOS codec profile. You see that list of supposedly supported codecs on the specs page? It's a lie.
The Archos on the other hand, the list of codecs on their tech page is what their android tablet actually supports. If you've got a 720p h264 MKV with subtitles. It'll run. If you've got an FLAC sound track. It'll run. Is your media on your cellphone? Take out it's memory card, stick it in the tablet, and it'll run.
Another thing that you can do on an android and not on an iOS. The apps aren't compartmentalized. When my sister wanted to see if my android can display Excel files. I searched google for any XLS, downloaded the RAR, and then opened it in another app to extract it before opening it in another app that can open the XLS. You can't do that on iOS. Try doing that on iOS and you'll get "Safari cannot download file"