iMovie Use your computer’s Multi-Touch trackpad
If you have a Magic Trackpad, or a MacBook, MacBook Air, or MacBook Pro with a trackpad that supports Multi-Touch technology, you can use a Multi-Touch gesture to expand or contract filmstrips in iMovie.
To expand or contract filmstrips:
Move the pointer over the Event browser or Project browser, and then pinch two fingers closed to contract the filmstrips, or pinch open to expand them.