Yes you can do that.
In PowerPoint, select the video you wish to trim. The "Video Tools" section will appear in the toolbar.
Click the [Playback] tab > Locate the "Editing" group > Click [Trim Video].
Within the video, move the green slidebar to a new start location.
Move the red slidebar to a new end position > Click [OK].
When finished, replay the trimmed video clip.
Hope this helps.
