I don't yet see how this would end the adblocker arms-race. If they don't send any additional data identifying where the ad starts, the video-player can't prev

I don't yet see how this would end the adblocker arms-race. If they don't send any additional data identifying where the ad starts, the video-player can't prevent the user from simply forwarding to skip the ad. If they do include metadata about where the ad is, adblockers can use that to cut it out.