Hmmm, 20000 lectures times 45 minutes (or more) times $1 per minute is 900.000 bucks. I would say that is not minimal. Also note that these videos haven't been recorded with publication in mind. Also I don't think you can add captions to a 45 minute long video in few minutes. It would take at minimum 45 minutes to ensure they are placed correctly (well, maybe you could watch at 2x speed and still have reasonable accuracy).