How to Trim Video Clips in Windows Movie Maker
You can fine-tune the duration of a clip in your movie by moving the clip’s start point or end point, or by changing the duration.
Extend or shorten a clip in the timeline by dragging
In the timeline, drag the edge of the clip you want to extend or shorten.
Extend the clip: Drag the edge of the clip away from its center.
Shorten the clip: Drag the edge of the clip toward its center.
Use the trim editor
You can use the trim editor to fine-tune when your clips begin and end,it will help you trim the video clips with millisecond accuracy.
Click the video clip to active it, when it shows a yellow box click the "Trim" icon at the middle menu bar.
The trim editor appears, presenting an expanded view of your outgoing and incoming clips. Move the two edges of the yellow box to set the start time and end time, or input the time, The video between these two edges will be reserved. When you’ve finished trimming the clips, click "OK" to close the trim editor.
To trim again or remove the trim effect, drag two edges can be work.