What an interesting comment. I also find that there is a lot of not great learning materials available. Perhaps it is not surprising, but the really quite goo

What an interesting comment. I also find that there is a lot of not great learning materials available. Perhaps it is not surprising, but the really quite good is uncommon. And, I expect that poor materials lead to poor learning, missed things, misunderstood things, etc. But another point is that the presentation is not the main place where people learn, at least in math, which is the field I teach in. The main place people learn is in doing the exercises. I will pull a number out of my posterior and say it is 80% exercises (a matter of opinion, I concede, but what else can you do with opinions besides spread them around?). Obviously twiddling with video speeds doesn't apply at all to that.