Editing a project that involves webcam footage (MPEG, MPEG-2 Video, AC3) plus clips downloaded from YouTube (MPEG-4, H.264, AAC).
Everything plays just fine in FCP6, but once I export, a few of the clips no longer show. When QT Player reaches one of the faulty clips, the last frame from before the clip will freeze and stay on for as long as the clip was supposed to play. Audio is fine. Synch is still fine after the freeze. Uploaded to YouTube, something slightly different happens: the faulty clip is replaced with a blank gray screen.
Interestingly, if I open the exported video in FCP6, it's actually worse: video loops back on itself, ends up way out of synch, etc. Audio still fine.
Yes. You are trying to edit MPEG, MPEG-2 Video, AC3 plus clips downloaded from YouTube (MPEG-4, H.264, AAC). FCP doesn't work with those formats natively...they are unsupported. The problem is that it APPEARS as if those will work in FCP...but they will not. A host of issues can arise, most at the final export phase...and this is one of them.
FCP requires that all footage be converted to an FCP editing codec, like ProRes. This is a must...BEFORE you edit. If you want to edit those formats natively, you need to use an edit system that supports doing that...like Premiere Pro.