iMovie now only supports videos in the formats as the picture shows below. If your videos are in these formats, you can import them to iMovie for editing easily. If not, please click the corresponding format below to get a solution.
iMovie allows you to export the edited video in the following formats: DV, AIC, QuickTime Movie (.mov) and AAC.
It's the easiest video editing tools for video editing novice to create stunning professional-looking videos on Mac (macOS 10.13 High Sierra included) and Windows.