I'm having problems playing some files in the source window of Premiere Pro. Everything plays perfectly in the small preview window in the top left corner of Premiere. But when I try to play them from the Timeline some files play without audio, some files play but with stuttering video and some files just come up as a black screen. I can't find any one common factor which would explain it - I mean why play perfectly in one part of Premiere but not play in another. How does THAT happen? I've set Premiere to playback on desktop only rather than through DV hardware.