Thank you, but in the meantime, I seemed to have found the culprit:, which is the way how Explain Everything records the lectures: it pauses recording in between the slides (according to Explain Everything “the pauses are caused by stopping and starting the framework that records audio clips for us”) So, there are these silent parts, a few frames in duration, every time the professor advances slides, and the silence makes it impossible to sync the footage. It’s not the VFR vs CFR, or 30 vs 29.97 issue.
Now, I have a daunting task to identify all of these pauses, delete them, join the clips together, and I bet they would sync up without any issues.