I am not for ads but what is so difficult about adding them to the video stream. This should make adblockers useless since they can't differentiate between the video and the ad. I could just imagine it would be difficult to track the view time of the user and this could make the view useless since they can't prove it to the ad customer. I have no in depth knowledge about hls but as I know it's an index file with urls to small fragments of the streamed file. The index file could be regenerated with inserted ad parts and randomized times to make blocking specific video segments useless.