IMovie REALLY Slow

Question

I have recently been encountering problems with iMovie. When I import a file into a project in "DV" format. It takes about 75 minutes. I have no problem with that. However, the file that I import is in MPEG-4 format. I realized that I could be saving myself time and disk space by importing the file into an iMovie project in "MPEG-4" format. The file imports fine, but that's where the problems start. Trying to edit the imported file in the "MPEG-4" iMovie project in a nightmare! It takes 30 seconds or more just to split a clip at the video playhead. The playhead will not move smoothly when I drag it using my mouse, whereas it moves smoothly in projects created in "DV" format. When I try to move forward or backward frame-by-frame using the arrow keys, it is really slow to respond. I have plently of free memory and there is no CPU intensive task going on while I am trying to do this. I do not experience any of these problems with iMovie projects in different formats (ex: HDV, DV Widescreen, DV, and iSight). This leads me to believe it's a software issue, but I haven't been able to solve it yet. My post in the iMac forum:
http://discussions.apple.com/thread.jspa?messageID=4171998#4171998
suggests that it's a fragmented HDD that's the problem, but my iMac is just fine. It isn't slow at all. Even iMovie isn't slow when editing in other formats. Only in "MPEG-4" format do I encounter these issues. Any help is appreciated.
Trevor

Answer 1

Yes, it's much larger (in bytes), but DV lends itself to editing, while MPEG (1, 2 and 4) does NOT.
Hi Lennart,
Is this because the compressed formats generally require "on the fly" decompression and recompression to allow editing? (I've been trying to follow up on Trevor's problem and can find quite a few comments on the net indicating that people are having similar problems with slow editing of Mpeg-4 in iMovie, but can't find anywhere with a good explanation of the reasons for it).
Cheers
Rod