I have some M-PEGS which are classed in the propereties as video clips. Some convert in TMPGE but some won't, even though they are all classed as video clips. The ones that won't convert, are these already VCD files? Also how do you enque clips to convert?
First of all, you should avoid re-encoding video files as long as possible, because the quality will suck. My guess is that the files that don't open are either damaged (yeah, they play OK with MediaPlayer, etc, but TMPGEnc requires 100% working files) or they have "weird" audio (like AC3) that needs to be decoded first. Sure all the clips you've tried were with extension .mpg? The "Video clip" crap in Windoze doesn't tell a **it, I can configure Win to say "Video clip" for my textfiles as well.
