It takes longer, but the best presentation of this kind that I've given was from taking video of a live coding exercise and editing it extensively (removing typ

It takes longer, but the best presentation of this kind that I've given was from taking video of a live coding exercise and editing it extensively (removing typos, adjusting speed). Then split it into sections and made a sequence of short clips out of them. Then put that into a presentation with one clip per slide. That way if I was a little slower when talking than planned, the video wouldn't get ahead of me, it would reach the end of the current clip and advance once I brought up the next slide. It's a lot of work but it comes out looking effortless, and without wasting any of the audience's time.