ALL video plays in slow motion in viewer and timeline (but not audio)

Hi all,
I've been using FCP7.0.3 for a couple years now, and have never gotten this behavior:

All videos that I've downloaded from youtube in MP4 format (the only format I can find) are playing totally out of sync; the video is in slow motion and the audio plays at regular speed. This is even true of clips that I've used before. Video that I downloaded from camcorders and my iPhone, however, work just fine.

I read on a forum that MP4 is not a good editing format, but it's worked perfectly before tonight and now it's gone all wonky. Is there something I can change in the settings? Files I need to delete?

Thanks,

Will

If it has worked before and it doesn't work anymore, even with old files that did work, you might consider trashing your preferences. Or see what has changed in your system. Have you updated your hardware, OS or other software? Are you using a different workflow now? Hard to say with so little information.

No change in OS or workflow. How do I "trash" my preferences?

Some troubleshooting tips: support.apple.com/kb/TS1846

"Preference Manager" is free from Digital Rebellion, and will trash your pref files quickly, safely, and properly.