Using video in PowerPoint
Incorporating video into a PowerPoint presentation can be an effective teaching strategy. With video you can replay a historic event, demonstrate a concept involving motion, dramatize a theory, show an activity filmed far away, slow down motion, or replay action. A growing collection of readily available video is posted at websites like YouTube, the Smithsonian, and Wikimedia Commons. There are literally tens of millions of clips to choose from!
Here are three ways to incorporate a video clip into a PowerPoint.
1. Link to a web page. This is generally the easiest and least problematic choice. Type a web address on a slide and PowerPoint automatically converts it into a link. You can also select text or an image on the screen and choose Insert >> Hyperlink. When you present the slideshow, clicking the link leaves PowerPoint and launches a browser showing the page you indicated.
BEFORE WE GO ON: In order to use strategies 2 and 3 you need a video file, and it needs to be in the same location when you play it as when you inserted it. To avoid problems, create a new folder for the presentation and store your PowerPoint and video files there. Different platforms like different types of files. Macs prefer .mov files, and PCs like .wmv — an .mpg or .avi should be friendly to both.
2. Link to a video file. Choose Slide Show >> Action Buttons >> Movie. On the on slide screen, click and drag to draw your button. In the Action Settings dialog box, click “HyperLink to:” and choose “Other file:” on the dropdown menu. Select the file to want to play and click OK. When you present the slideshow, clicking the button takes you out of PowerPoint and opens the video in a player.
3. Embed the video on a slide. This is prettier, but trickier. Choose Insert >> Movie and select a file. This creates a viewer box on the screen that is either activated automatically when the slide is displayed or requires a click to start (press space to stop). Remember that the video is not saved in the PowerPoint file; you need the video file as well as the PPT when you present.
FINAL WORDS: You should have few problems if you use the same computer to create and present slides. However, I strongly encourage arriving in the classroom a little early to test that all videos are set up correctly.
P.S. You can learn more about PowerPoint here.
NspireD2: Learning Technology in Higher Ed. 
I’m not sure what you mean by “a video that is playing across slides” – like a soundtrack? I didn’t know you could do that with video. I thought a video always stopped when you went to the next slide.
I did find this on pausing music: http://www.pptalchemy.co.uk/Pause_Music.html
and this controlling movie clips with buttons: http://www.ellenfinkelstein.com/powerpoint_tip_movie_buttons.html
I have a question. Is it possible to stop a video which is playing across the slides when one stops the slides. Suppose, there’s a movie that’s playing with the slides. I am previewing the slides and when I am on a specific slide, I stop the slides by pressing space bar. Is it possible to stop the video at that point as well or let’s say is it possible that the video would stop at that point automatically when I stop the slides from moving?