A flash client could use adobe DRM ( test here https://helpx.adobe.com/flash-player/kb/protected-video-content-play.html https://helpx.adobe.com/flash-player/kb

A flash client could use adobe DRM ( test here https://helpx.adobe.com/flash-player/kb/protected-video-content-play.html https://helpx.adobe.com/flash-player/kb/protected-video-cont... ), or even use a negotiation scheme that is harder to reverse engineer compare to javascript. current HTML5 standard do not defined a DRM standard. I would like to add that it is only a small part of the issue as the average user would not probably care but as you can see here ( http://www.quirksmode.org/html5/tests/video.html http://www.quirksmode.org/html5/tests/video.html ), downloading video is one right-click away. Youtube does some clever event interception to prevent this. But again the cost of a developer to replace the existing system, re-encoding the videos ( sources might have been lost ), might be too high for a "normal" website to update their content.