This idea of adding a question is nice, we already have a question sortcode to add questions in the units, but mark complete if the answer is correct is not easy to implement and it also has many loopholes.
As mentioned by Mr. Vibe we will be developing a plugin for youtube videos, so you can wait for this.
You can also add assignments in the units and assignments are manually evaluated. Enable the assignment lock from the course manager->assignment lock, and now user cannot go to the next unit until you evaluate the assignment.
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