Is it possible to play a video while presenting using the keyboard without having the use of a mouse?
if I understand you correctly you could use the right and left keys on your keyboard and the Page Up/down keys to present the Prezi - this would be equivalent to using the mouse on the arrows under theviewing window of the Prezi.
In full screen mode you can also drive forward using the space bar see here.
Of course you must also have path points in your Prezi - putting a path point directly on to your Video (no frames) would autoplay it when you arrived there.
hope this helps
Many thanks for your answer it was very helpful.