- You can’t do it in iMovie ‘08. (I think the newly announced iMovie ‘09 can do it, but it’s not yet available.)
- Final Cut Express or Pro can do it, but they’re expensive. If you happen to buy or pirate one of them, good luck getting the output to be progressive.
- Quicktime Pro can do it, but the output quality is abysmal.
ffmpeg on the command line has come to the rescue. With this method, I was finally able to do something that I thought should be a simple task: take this input video and output a video that consists of one of every X frames instead of every frame.
I can’t believe how much time I spent today trying to properly construct a trivial, meaningless 45-second video.