Sincerely I don’t think there’s much difference in effectiveness between both techniques. One thing is clear, in the live class you feel more special and you may be more focussed in what the other person is teaching at you. On a recorded video you can get distracted by something else and then rewind (can we still use this word when talking about youtube?) and play it again.
How to mesure a difference in learning? This is highly dependant on what you want to achieve. Someone who is able to repeat a task or someone who besides repeating the task is able to overcome problems. Probably we prefer the later.
The starting condition is that a group of student have seen the execution of a task from a 3 minute recorded video, whereas another group have seen the same task being executed live in the same amount of time with room of questions. After letting them to familiarise with the new method learnt we will proceed to measure their learning with a n number of problems where the same technique needs to be applied, but varying slightly and progressively the knowledge in the task asked (eg. not all the steps are needed, or extra knowledge like arguments are needed). Recording for each of the exercise the steps taken and the time to solve the task could provide a estimation of which teaching method is more effective.
From my point of view both are going in general to match on efficiency, and the learners that get the high score would be invariant of the teaching method as they will more from the self-learners category and they will find their way.