The other idea Ive thought of is an overlay that somehow embeds the user name on your site, and their ip into the video, or somehow creates a watermark righ on the video itself for every download. Video gets downloaded and ends up on any tube site or torrent without permission that user gets their account canceled and then maybe a way to blackball that member from signing up, or else allow signups but have restrictions. These are all things that can be done, but require it to be done industry wide, and to have a large financial backer to get them implemented. It isnt easy to close pandoras box...
Oh and 50 solutions that no one will adapt to cause they are scared to change...