Basically if it plays in iTunes then there's a decent chance it'll work in AppleTV. Time will tell.
If it plays in iTunes WITHOUT INSTALLING ADDITIONAL CODECS, it will play on the AppleTV. Unless enterprising people figure out how to hack codecs into the AppleTV, you'll be stuck with H.264 or MPEG-4 SP only for video.
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
Video formats supported: H.264 video, up to 1.5 Mbps, 640 by 480 pixels, 30 frames per sec., Low-Complexity version of the H.264 Baseline Profile with AAC-LC audio up to 160 Kbps, 48 kHz, stereo audio in .m4v, .mp4, and .mov file formats; H.264 video, up to 768 Kbps, 320 by 240 pixels, 30 frames per sec., Baseline Profile up to Level 1.3 with AAC-LC audio up to 160 Kbps, 48 kHz, stereo audio in .m4v, .mp4, and .mov file formats; MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per sec., Simple Profile with AAC-LC audio up to 160 Kbps, 48 kHz, stereo audio in .m4v, .mp4, and .mov file formats
I agree.Okay, this Apple TV keeps getting less and less interesting.
I agree.
And to mkrishnan's point a few posts back, my Mac mini is getting more and more interesting now that it has the Perian codec on it that lets Front Row play just about everything.