CompuServe Messages

The first thing that comes to mind is that audio has a data rate too. Your system will have some data rate max. That could be a few hundred kb/sec or it could be a couple of MB/sec if your system is really moving. Whatever it is, to play a video file the system needs to maintain some data rate for that file. If you then add audio your asking the computer to pump through a yet higher data rate. If that get over your systems capabilities than you'll get that video break-up. Unlike MPEG, most AVI or QuickTime compressors don't compress audio. That means the audio file could be adding a sizable data rate demand.