If you are importing the mpeg in to MM, then it doesn't work well with this
file type and audio only is a common problem. Convert the mpeg to avi and
import these files. All should then be fine.
If you don't already have a utility for
converting from MPEG to AVI, I suggest
trying TRex.
It runs very nicely as a background task, as it
runs by default as a low-priority task. I was
able to continue *working* while it silently
ran in the background. Nice tool!
Here's a download link I found. It costs $14
if you want to keep using it after the 60-day
trial period expires.