I have some .mpg files on my computer that do not play correctly in Quicktime, vlc, or MPlayer. What happens in QT is I will play the file but it will only play a fraction of the movie and it will end ...

624x352 is 16:9 and 720x480 can either be 16:9 or 4:3 depending on what you set the encoder to. Which aspect ratio do you want the MPEG2 file to be in? If it's 16:9 there should be no black bars at ...