iMovie stabilizes video by analyzing the camera motion in the video and then moving the picture the opposite way to steady it onscreen. In this process, iMovie zooms in on the picture slightly. The amount of unstable motion in the clip determines how much zooming is necessary.
Zooming in crops out some of the picture, but you can fine-tune the level of stabilization to strike the right balance between keeping the video steady and retaining as much of the picture as possible.
When you move the pointer over a video clip in a project that has been analyzed for stabilization, an icon in the upper-left corner of the clip shows the level of stabilization:
Hand with black background: The clip is fully stabilized and required little to no zooming.
Hand with orange background: The clip is partially stabilized and required extra zooming, so some areas of your video may be cropped out.
Hand with red background: The clip is partially stabilized and required extensive zooming, so more of your video might be cropped out.
Hand with red background, with a slash through it: The clip couldn’t be stabilized.
To adjust the zoom level in stabilized video:
In the Project browser, double-click a video clip in a project that has been analyzed for stabilization.
Note: You can’t adjust the stabilization level of video clips in the Event browser.
At the top of the inspector that opens, click Clip, and then drag the Maximum Zoom slider.
Zoom in (move the slider to the right) for greater stabilization. Zoom out (move the slider to the left) to show more of the picture.