You either have to link to the content somewhere else, or embed it into the presentation itself. In both cases, you have to hope and pray that something in the technology chain doesn't break down while you're trying to give your presentation. Which is the technical reason why I tell people to avoid such things.

There's also the more philosophical reason. Being that while PointPoint type presentations can be powerful and useful tools, it's very easy to turn them into pointless sideshows with lots of images, animations, sound effects, videos, and what not. The more of these things you put into a presentation, the more you dilute any meaningful content that you might have wanted to convey. I would suggest a complete rethink of the way you're going about showing this video. Also ask yourself if it serves an important purpose to the presentation as a whole. If the intent is more to entertain than inform, leave it out.