you can use a converter like
ReduxEncoder, or an online converter tool like
Zamzar.
Use
File -> Import Movies… to select your converted video. iMovie will analyze the video and generate thumbnails, so this can take a few minutes for larger video files.
Before we’re able to use the video, you’ll need to add it to your Project Library from your Event Library. Just make sure you select the whole clip, and drag it over to the other side of the screen.
Now deselect the clip from your Event Library, and select the copy in the Project Library. To rotate your video, open the Crop menu, make sure it’s set to ‘Fit’, and use the rotate buttons. When you’re sattisfied, press Done.
You’ll notice that you’re video has now been rotated in your Project Library. To export it, go to
Share -> Export Movie… or press cmd+E.
As with Windows Live Movie Maker, you can also upload your rotated movie directly to
YouTube, or your personal MobileMe Gallery.