Trimming clips in Apple iMovie

iMovie’s approach to trimming is typical Apple — simple and effective. iMovie uses the preview window for clip-trimming operations. If you look closely at the lower-left corner of the preview window, you’ll see two tiny little triangles. These are in-point and out-point markers; you can use them to trim clips in the timeline.
To trim a clip, follow these steps:

1. Click a clip in the timeline to select it. When you click the clip, it should load into the preview window. If it does not, make sure that the desired clip is actually selected in the timeline. The clip should turn blue when it is selected.
2. Click-and-drag the out-point marker in the lower-left corner of the preview window to a new location along the playback ruler.
3. Click-and-drag the in-point marker to a new position if you wish. The selected portion of the clip — that is, the portion between the in and out points — will turn yellow in the preview window playback ruler.
4. Choose Edit>Crop The clip will be trimmed (cropped) down to just the portion you selected with the in and out points. Subsequent clips in the timeline will automatically shift to fill in the empty space on the timeline. If you trim a video clip from which you have extracted the audio, only the video clip will be trimmed; you’ll have to trim the audio separately.