For example, if you added a video clip that’s 20 seconds long, you can’t make it longer than 20 seconds. If you can't drag the edge of the clip, it means there is no additional video at the beginning or end of that clip. The arrows indicate which directions you can trim the clip:

In the timeline, hold the pointer over the beginning or end of the clip that you want to trim until your pointer becomes the clip trim tool.

When you zoom in, you can see more detail in the clip, which can make it easier to edit.

To zoom in on the clip, choose View > Zoom In, press the Command–Plus sign (+), or pinch the trackpad.

With your project open, scroll the timeline to locate the clip you want to trim.You can trim a video clip or a photo so it appears for a shorter or longer period of time in your movie. It might also mean the clip is at the shortest length allowed by iMovie, which is 0.3 seconds. If you still want to change the duration of a clip, try changing the speed of the clip. If you can't drag the edge of the clip, there might not be additional video at the beginning or end of that clip. For example, if you added a video clip that’s 20 seconds long, you can’t make it longer than 20 seconds. To make the clip shorter, drag the edge of the clip toward the center of the clip.To make the clip longer, drag the edge of the clip away from the center of the clip.Drag the beginning or end of the clip to make the clip shorter or longer:.To zoom in on the clip, pinch open in the center of the timeline.A yellow highlight appears around the selected clip.

With your project open, tap the video clip or photo in the timeline.You can trim a video clip or a photo so it appears for a shorter or longer period of time in your project.

Split clip in imovie