Front Row ? Apple TV ?

What format does Front Row use when playing movies. I have clips from youtube and such which I would like to use in Front Row but it doesn't play those files. It will play things downloaded from iTunes... Any Help

I am also looking at investing in to an Apple TV, but as far as I can tell it runs a similar program to Front Row, would I have the same problem?

it plays mpeg files, mov files, and avi files. Not flv files though. im not sure about other video files, but for me, it plays those files. They are the only files i have in itunes anyway!