Generally there are two methods:
Method I:Play the PowerPoint offline
1.to download Youtube video with the free software Leawo Free YouTube Download
2.then convert the Youtube video to avi format with Leawo Free AVI Converter
3.insert the avi video into PowerPoint
Step 1: On the Insert tab, point to Movies and Sounds, and then click Movie from File.
Step 2: Click the video you want to use and then click OK.
Step 3: After you click OK, you' are promoted with a message asking how you want the movie to start in the slide show. I recommend you choosing "Automatically "even if you want the movie to play when clicked. And that's done.
1. This is the easiest way to insert a video.
2. When playing the video that is inserted in this way in the PowerPoint, it only shows the video picture, and only has two control options: play or stop. So you can't select the playing time freely
3. Only video in formats of AVI, MPEG and WMV can be inserted in this way
4. Always put the movie in the same folder as your PowerPoint presentation.If you later move the PowerPoint presentation to another computer, copy the movie too. Keeping your movie in the same folder as your presentation ensures the link will still work. However, you should always test the movie on a new machine just to be certain. Re-insert the movie, if necessary.
Method II:Play the PowerPoint online
You need four steps to make it:
Step 1: Get URL of the video
Step 2: Insert the ActiveX Control Shockwave Flash Object to your PowerPoint
Step 3: Add the the video link to your PowerPoint
Step 4: Fine tune the video in your PowerPoint file
More details can be found at How to play Youtube video in PowerPoint 2003/2007?
Related:PowerPoint to DVD PowerPoint to Video PowerPoint to FLV