I find that most videos showing underwater activity for instructional purpose are really bad.
Almost no "actor" is kicking properly, breathing properly, keeping a proper attitude and trim, and behaving as I would behave on the same situation.
Of course, there is not only one "correct" way of doing things, and I watched these video exactly for seeing how "others" would face the same tasks (for example, how to swim backwards inside a tunnel, or how to reach easily your valves when back-mounted).
Simply I find systematically very objectionable behaviour being summoned as "the truth", and so I am generally Quite sceptic on the possibility that a novice can really learn something useful in these videos.
More easily, a novice will try to imitate these wrong behaviours, and then the instructor will have to make an hard job for converting back the student to proper skills.
On the other side, I find very useful to watch other kind of videos, not "didactical", but showing great divers in action, for example free divers when performing records, or simply diving for pleasure.
I would recommend the videos of a couple of french free divers, Guillaume Nery and Julie Gautier.
They mostly do not even use fins, and still move with elegance and efficiency, proving that it is not the technical equipment making a great diver. Here a couple of examples (when you see Guillaume, the cameramen is Julie, who also records the video while freediving - and vice versa, of course):