Live video feature in Keynote

Hi. I love the newish "Live video" feature in Keynote where I can use my Face Time camera to show me speaking on any one or all of the slides. It's great being able to position and resize and zoom in on my video. The slides look great. Unfortunately, on playback—whether using "Play Recorded Slideshow" or exporting the presentation as a movie and playing it back in Quick Time—the Face Time video is horribly laggy, so much so that the image changes in jerky fashion and there is no sound at all. I tried this several months ago, then again today. The result is the same. I'm using a 2017 Macbook Air 1.8 GHz Dual Core i5 running Big Sur 11.1.

What could be the problem? Do I need more computing power for this feature?