Hi
On my PC MPEG4 clips always play ,,,,,but the sound plays back at the correct speed whilst the video lags progressivly behind with longer clips.It's even worse with the bigger formats. NCH say its a PC performance related problem. MPEG4 HD 1080 or 720 would seem to require a lot of unpacking but the sound can be played more easily.
I convert all my clips to MPEG2 before I edit and this plays OK.
The star and the box are for adding effects etc to the clips concerned. Click em and see!
Nat