After starting Totem in Ubuntu 12.10 (playing an .MTS file), it starts out playing just fine, but after about 3 seconds the sound goes away. No clue at all what is happening. .MPG files play just fine.
The videos play just fine, with sound, in VLC.
EDIT: Pausing the video and then starting again brings sound back for about one second, and then the sound fades again.