If a video file contains an incompatible video codec, the file may not import or play correctly in iMovie ’09. In this case, you may need to convert the video file. You can use QuickTime Pro to convert many types of video files. If you do not have QuickTime Pro, you may need to either purchase QuickTime Pro or download another video conversion application not manufactured by Apple.
iMovie '09 supports most commonly-used video codecs, including DV, MPEG-2, MPEG-4, H.264, and AIC.
In order to identify a video's codec, open the video file in QuickTime Player and choose Show Movie Inspector from the Window menu.
To use QuickTime Pro on Mac OS X v10.6 Snow leopard, you may need to install QuickTime Player 7 and then enter a registration code.