YMMV with Apple TV. Specs are here, http://www.apple.com/appletv/specs.html

If you're like me, it will play about 10% of my collection. WDTV Live, on the other hand, plays everything.

If you're in the Apple eco-system, Apple TV is great. For those who aren't, it's Apple's way or the highway. I'm half in Apple, half out of Apple, and it's a total nightmare.