Books are pretty good, why bother with movies?

Although I agree with you, this comment is missing the mark. Books and films are two fundamentally different mediums and have two different audiences, while this is more about supplementing the text version of something with audio/video.

I think that an audio (or video) version would be superior, but more because, assuming there are captions, the audio might be able to describe something beyond the code alone more easily than typing out a note would.

It takes lots and lots of effort to turns books into movies and vice versa.

You don't just take a transcript of the dialogue in the movie to make a book.