I have a youtube channel with animated maths videos that I have created, and I would like to create some Udemy courses covering similar topics.

The Youtube videos are typically about 5 minutes, and I would expect each course to be the equivalent of 10 to 20 of those videos.

I know I can't just use the Youtube videos because you aren't allowed to charge for a Udemy course if the material is available for free elsewhere.

I just wondered, how different does the course need to be? The existing descriptions and animations are the best way I can explain the topics.

Is it sufficient to reword the voiceover and change the appearance of the videos while keeping the same animations and concepts? Maybe add some extra videos and downloadable content too?

I'm not trying to game the system, but equally I don't want to change everything so much that it becomes less useful than the original.