MP4 and QuickTime Issues

After creating my instruction modules in Camtasia, I exported them as .mov files. Then in QuickTimePro I converted them to MP4 files (supposedly the new format for video podcasts) and posted them on my site. But I'm having the darndest time with them. Approximately 60% of the time QuickTimePro encounters an error and shuts down the browser completely. Sometimes if you open the browser and file again it will work - but sometimes not. This is extremely frustrating because I don't see a pattern. The error message is: An error occurred inside a plug-in contained on this page Maybe this relates to MIME or mismatched versions of QT extension for .dll file. So I am just going to throw out these MP4 files and stick with .mov files and .MP3 files only. But it leaves me asking what is the MP4 format for? What benefit does it have over an .mov file? More compression? (I don't think so). Any thoughts welcome