according to my experience, imovie can not import all kinds of mpeg4 files, some mpeg4 or mp4 files will not be imported to imovie.
maybe the following article will explain why imovie including '11, '09, '08 can not import mpeg4 and also this article will also provide a way to solve this problem if it is really the video format problem.
why not have a try to test if it is the video format issue?
i hope it helps more or less
MacBook Pro / Intel Core 2 Duo / 2.4 GHz / 2GB RAM Mac OS X (10.6.1)
I own a Sony Sony Cyber-shot DSC-V camera. Video files it creates are supposedly in MPEG1 format (according to the info pane in iPhoto). I use MPEG Streamclip to convert the files to either mp4 or dv format.
iMovie 09 is supposed to recognize both dv and mpeg4 files, and it does that just fine on an Intel computer at the local mac store.
My macbook pro with Mac OS 10.6.1 and iMovie 8.0.5 (820) however, does not. I have deleted the iMovie 09 application, removed all iMovie "receipts" and reinstalled the program without success. Reinstalling Snow Leopard has also not resolved the issue. Importing dv and mpeg4 files to iMovie from a new user account didn't work either.
From what I can tell, my Snow Leopard upgrade DVD is unable to perform an "Archive and Install". The mac store told me if Mac OS 10.6 is already installed on a computer, that the installer will automatically perform an archive and install. An Archive and Install did not happen on my machine when reinstalling Snow Leopard.
The Mac store now recommends that I initialize the hard drive and begin with a fresh install of Snow Leopard. For obvious reasons, this is an option I wish to avoid.
Pulling my hair.... Any help will be appreciated.