Cropping a Video Clip
You can select only a portion of a clip that you actually want to play in your movie by cropping it - shortening it either at the beginning or at the end or both - and deleting the unwanted portions of the clip.
Note: If you make a mistake while editing a clip, just press the Apple/Cmd key and Z, or in the menu at the top of the screen select Edit...Undo, and you'll undo your previous move. You can undo the previous 10 steps.
Note: This is not an iMovie-specific trick. Cmd-Z always means Undo in Macintosh applications. On Windows, Ctrl-Z does the same thing.
To crop a clip, first make sure the Mode button on the left is in editing mode by clicking on the icon on the right that looks like a pair of scissors.
Now select a clip in your Viewer by clicking on it.
Notice that a blue scrubber bar appears just below the Monitor area where the clip is displayed. And on the top of the scrubber bar is a small gray inverted triangle, marking a point in the clip. This triangle is called the Playhead.
If you pass your mouse over the scrubber bar, you'll see two tiny triangles appear on the far left that are called crop markers. These are what you use to crop your video.
Click on the right crop marker triangle and drag it to the point where you want the clip to stop. The Playhead also will move to that point in your timeline.
Now click on the left crop marker triangle and drag it to the point where you want your clip to start. Again the playhead will move to that point.
You'll notice that the color of the video track above changes from blue to yellow as you drag. This yellow part is the part of the clip that you're saving.
Now in the menu at the top of the screen select Edit...Crop.
The blue parts of your clip on either end will be deleted and will disappear (this is another good reason for copying your clips into the Timeline Viewer instead of just moving them there, so you still have the original clip intact on the Shelf.)
Also notice that any clips that are on either side of the clip you cropped also have moved in to butt up against the cropped clip and preserve a continuous timeline.