Quote Originally Posted by jmcc View Post
No, I don't have any problems with 720p trailers appart from the sound thing: for example, Lara Croft: Tomb Raider. I have no sound with this 1080p teaser on my PC.

Also there is at least another 720p trailer with no sound on my machine with VLC but in these cases I use Kaffeine (a media player in Linux) to have it playing with sound.
Per the PM I sent you, the Encodes work fine for me, the problem appears to be local to your machine. The only thing I can suggest is to try to update your players to the latest versions, or try a different one.
In this case, try the latest QT Player, to narrow down the issues. Dont rule out drivers or hardware either, even conflicting DLL's will give you a headache.