Hello! Sometime last year, this problem began with iMovie '09 on my old iMac, and has persisted into '11 on my new iMac. When I am in iMovie, I can see thumbnails just fine. When I scrub or play footage, however, no video appears in the viewer. I can hear audio, and what is especially weird is that iMovie still acknowledges that there is color there (things like the white balance eye-dropper detect color) and the histogram reflects color, but I can not see any. I have been searching all over for a solution and can't find it. I've dumped whatever caches I could find, reinstalled the software, repaired disk permissions, etc. This footage is fully compatible with iMovie - it's mostly shot on the iPhone 4. Any help? Thank you!