So in the past year, I've come across a very strange quicktime problem - twice.
The first time, I had a set of 20 random quicktime clips that would not play in Snow Leopard. I had the clips backed up on 2 separate drives, and those, too, would not play when imported. The file sizes were the same. I figured the files somehow got corrupt (even on the backups, which still seemed unbelievable).
But then I took those clips to a completely different Mac with the same OS, and they would play.
Same thing happened today on Mountain Lion. 6 completely random clips (and their backups) would not play video on my system (audio only this time, no video), but play fine on another.
Any ideas why these clips refuse to play on a certain machines?