TV sound does not work when using non-iTunes media

I cannot get sound from my TV when I use non-iTunes media through ATV. I am trying to play a home video based on my Mac to my TV through ATV, and the picture is fine. Sound, however, only works on the Mac. If I restart the computer, the sound streams with the video with no problem. Anyone else have this issue? I thought that maybe there was a conflict with iTunes, but I still have the problem even if I shut iTunes down.