iMovie doesn’t just take still photos; it can also dish them out. It can grab selected frames from your footage, either for use as frozen frames in your movie or for exporting as graphics files. (You might want a still frame to end a Ken Burns zoom, for example, so that the camera seems to hold still a tad longer after the zoom.)
The Edit → Create Still Frame command creates a still image, in the Clips pane, of the frame currently indicated by the Playhead. You can use the resulting still clip just as you would any still clip: Drag it into your Movie Track, apply effects or transitions to it, change its name or duration, and so on.
One of the most obvious uses of this feature is the freeze-frame effect, in which the movie holds on the final frame of a shot. It’s a terrifically effective way to end a movie, particularly if the final shot depicts the shy, unpopular hero in a moment of triumph, arms in the air, hoisted onto the shoulders of the crowd. (Fade to black; bring up the music; roll credits.)
Here’s how you do it.
These steps assume that you’re creating a still frame from a clip that’s already in the Movie Track. It’s possible, however, to create a still frame from a clip that’s still in the Clips pane.
Position the Playhead on the frame you want frozen.
If it’s the last shot of a clip, use the right and left arrow keys to make sure you’re seeing the final frame.
Choose Edit → Create Still Frame (Shift-⌘-S).