Allow timing ads as part of the subbing process
Have you considered allowing subbing teams to define appropriate time points for ads to play? You could require that these breaks be distributed throughout the video, rather than shunted to one end, of course. In this way, ads wouldn't start playing midsentence. This would greatly enhance the ad-inclusive viewing experience, without removing the incentive to buy ad-free access passes for those who can afford them.
Just a thought.