If your PowerPoint video is a little long, there is very good news for you. You can trim videos within PowerPoint, no other software is required.
Go to the slide with your video and click on the video to highlight. On the Video Tools Playback tab click on the Trim Video icon to open the Trim Video dialog box. To trim the beginning of the clip drag the green Start Time marker. To trim the ending of the clip drag the red End Time marker. You can make your video as short as you like!