Flicker on playback when switching focus between streams
I'm recording videos with powerpoint presentations, and want to occasionally switch to a 'talking head' shot of myself, away from the slides. I've found a way to do this by having my main screen and integrated camera both as secondary streams, then using the focus tool in the editing step.
However when I play back my edited video, the transition from talking head to main screen, or vice versa, is not smooth. I see a flash of other images, just a frame or two, from the recording, perhaps from the start of one of the streams (??) and this looks a bit unprofessional, spoiling the effect of cutting to the headshot.
What am I doing wrong?! Any advice would be gratefully received!