What happens when you attempt to capture the Window the video is being played on using native applications; i.e., using screenshots, and capturing audio output to your speakers or headphones?
HTMLMediaElement already does not allow capture of audio or video when the src is set to cross-origin URL.
For WebRTC, we can read the raw data of a MediaStreamTrack itself using MediaStreamTrackProcessor.
If you believe that you can use a single approach or multiple approaches, including encrypted media (https://www.giacomovacca.com/2017/01/analysing-opus-media-from-network-traces.html
"This only works if the opus payload in the RTP is not encrypted"), to reliably prevent users from capturing and recording media being played on their
machine kindly advise me of that approach so that I can proceed to experiment with approaches to circumvent such restrictions.
For the above reasons, while specifications might advertise such capability as your requirement, the technology exists to thwart such limitations or restrictions, thus you cannot guarantee that the user cannot record the media they decide to playback on their machine. I suppose you could make such a guarantee, however, there is no way for you to verify that is true and correct for all cases.