iMovie Won't Import Video
You hook your camera up to the iMac and iMovie recognizes its presence. iMovie displays a blue screen with “Camera Ready To Record”. iMovie refuses to proceed any further with the importing of video and just sits there until you quit it.
The Problem
Unknown. Something has gone wrong deep within the bowels of the OS. Most of the lab can import video, it’s just these four iMac G5s that stubbornly refuse. It may have something to do with Core Audio.
The Solution
Launch Garage Band, play with the virtual keyboard a bit. Quit Garage Band and everything works perfectly. iMovie recognizes the camera and operates without a hitch.
Addendum
This is a true story. The names are unchanged to identify the guilty.

That’s horrible! What a nightmare!
We have one of those cameras at our lab, and it seems to work perfectly with our little laptop and desktop Macs, but I don’t know what kind they are. Probably older ones.
Hopefully it gets fixed in a patch or something.
It’s not a camera problem, it’s just that the iMovie app has some weird interaction (probably) with the audio subsystem. And as soon as you do the GarageBand thing the problem never recurs.
Hey thanks for that. I was struggling with that for weeks, and this trick fixed it in 10 seconds.
This had no effect on me at all but I wish it did. Does anyone know what the problem is? Please help.
Very frustrating.I tried the GarageBand trick & it worked once, but not anymore. I’m on a 800 Mhz G3 iBook running iMovie 4.0.1. All four of my other Macs run iMovie fine, including an older 400Mhz PowerBook. Go fig.
You are a genius ! This fixed my iMovie problem and my MPEG1 audio problem !! You saved me a lot of work and stress ! THANK YOU !!!