This thread is the first where I see such issues reported about video and sound being played back our of sync on the Halo 3 trailers. Thanks for bringing it up. I never encountered this issue myself and I watched all the trailers _many_ times.
It is also worth noting that all the high res trailers were encoded according to the same spec with the same bit rate, and are fecthed exactly the same way by the player.
I reported it for additional testing specifically in this area.