The QuickTime 6.4 upgrade contains a serious bug for users of Final Cut Pro 4. Based on several reader reports, it appears that any timeline in Final Cut Pro that mixes media codecs (for instance, DV media and LiveType titles) will not play, and the program will freeze requiring a force quit. One MacFixIt reader writes:
"Many folks are reporting that they cannot even open their projects. The QuickTime 6.4 ReadMe suggests upgrading to Final Cut Pro (mentioning DV improvements and better workflow). Obviously even casual testing by Apple would have revealed this bug prior to the release and they could have warned their hapless users."
Apple has now posted "QuickTime Reinstaller 6.3," which will bring the QuickTime software back to 6.3, eliminating this and other problems.
Some users are also reporting that they are unable to play MPEG2 files after updating to QuickTime 6.4. Reverting to version 6.3 fixes this problem in most cases.