Symptom: After having updated to the new firmware 2.3 for Apple TV, self-made HD movies including 5.1 Surround Sound will play but no sound can be heard.
Solution: This problem has been discussed much in Apple forums. The solution is very simple. Apple has even stated the solution in a support document, which can be accessed via this link: http://support.apple.com/kb/HT1755. What it tells you is that all video content containing an AC-3 sound track MUST contain another AAC stereo track for the same film, otherwise no sound will play.
Now, as videos containing an AC-3 track have to be in .mov format for the Apple TV to be recognized, another AAC track (even if it’s “fake”) can be easily added.
1. Open the affected movie in Quicktime Pro (or another app of your choice). Additionally, open a random AAC file.
2. In the Edit menu, choose Select All as well as Copy. Then go back to your movie. Now, again in the Edit menu, choose Add to Movie. If you open the Movie Properties via the Window menu, you should see that a new AAC file has been added to the film. Please deselect the tick on the left so that the sound of this track can’t be heard when playing the film on your computer.
3. As a last step, save your film. Now, the sound should play again on Apple TV.
Note: Apple intended to have a stereo and a Dolby track for reasons of compatibility. Next time, when you author or convert a movie with an AC-3 track, you may prefer to add a real stereo track for the movie instead of just a fake track.
You forgot one crucial instruction in Step 2: after you “select all”, you then have to copy. It’s a no-brainer, but I got stuck on it for a few mins.
Thanks!
@Paul: Thanks for the input! I’ve just corrected it.