If you use MPEG-4 video in an iMovie 5.0.2 HD project, you may notice that when you apply an effect, transition, or a title over a video clip, you don't hear any sound when you play back your edited clip. If you export the movie, the exported movie will also be affected. This occurs on computers with Mac OS X 10.4, or Mac OS X 10.3.9 with QuickTime 7.
To avoid this issue, extract the audio before applying the effect, title, or transition. Then reapply the sound after the video has been modified.
This document will be updated when additional information is available.