Each video clip in iMovie is represented by a series of thumbnail images called a filmstrip. Each thumbnail can represent several seconds of video encompassing hundreds of video frames (individual images).
You can expand the filmstrips to see more thumbnails in each clip. This expanded view makes it easier to select video more precisely. The most expanded setting displays one thumbnail image for each one-half second of video footage.
By contracting the filmstrips, you can see more video clips at once in the Project browser or Event browser. This contracted view gives you a better sense of the overall project and allows you to move clips within a project more easily. The most contracted setting represents each clip with a single thumbnail.
To expand or contract filmstrips:
Do one of the following:
Drag the clip slider to the left to expand the filmstrips or to the right to contract them. The number that appears to the right of the slider indicates how many seconds of video are represented by each thumbnail image.
The clip slider below the Project browser affects just the filmstrips in your projects; the clip slider below the Event browser affects just the filmstrips in your Events.
If you have a MacBook Air, or a MacBook or MacBook Pro with a trackpad that supports Multi-Touch gestures, 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.