Most consumer camcorders and still cameras include CMOS image sensors that expose the picture they’re recording progressively, instead of all at once. As a result, if the camera moves a lot during recording, or if the camera is recording fast motion, image distortion can occur. This causes the picture to appear wobbly or skewed. iMovie has a rolling shutter feature that can reduce this motion distortion.
To correct distortion caused by rolling shutter:
In the Project browser, double-click a video clip, or select more than one video clip and then double-click.
In the inspector that opens, select the “Reduce motion distortion” checkbox, and then choose a level of correction from the Amount pop-up menu.
Choose Medium for footage shot with a consumer camcorder. Choose High or Extra High for footage shot with a Flip camcorder or a mobile phone that records video.
If the selected clips haven’t yet been analyzed for stabilization, iMovie analyzes them first and then corrects for rolling shutter distortion.
To review the level of correction, play back the clip by placing the playhead (the red vertical line) in front of the clip in the Project browser and then pressing the Space bar; press the Space bar again to stop playback.
If the clip needs more correction, follow steps 1 through 3, this time choosing a higher level of correction from the Amount pop-up menu.
For information about analyzing video for stabilization, a process that corrects shaky motion in video, go to this topic: Stabilize video motion.