I gave Streamclip a try, as well as someone else's suggestion of simply re-saving the file in a .MOV container from within QT Pro. The .MOV file will load in iTunes and plays just fine there, but won't download to my aTV. QT doesn't give the option of saving out as an MP4, only exporting as such, which, even with an Elgato Turbo.264 and a dual 2-GHz G5 takes 10+ hours for a 1-hour 720p movie. Streamclip, on the other hand, seemed to have no problem saving the video track in an MP4 container, but didn't understand or couldn't read the audio track, which was encoded in AC3 format, and so stripped it out entirely. iTunes won't pass the MP4 file over to the aTV either. Did you do something else with your aTV? Hack it in any way? What codecs were the audio and video streams in originally in the file you converted?