Video playback out of sync

I have a video movie that plays fine on my Imac, but when I watch it on my Apple TV, it is noticeably out of sync. Given that it plays okay on my computer, it seems it must be something to do with the way Apple TV is playing it back. The movie is a feature MPEG-4 h.264 and is 1280 x 528. Other movies and video play fine on the Apple TV, but besides this one, I sometimes notice other video playing out of sync so I'm wondering what is causing this. I have an ethernet connection to my Apple TV as well, so it isn't slow wifi.