Lesson video on Cool is served through a signed link, not a public address. The link is generated on the spot, for that session, and doesn't work once copied out.
Over the video sits a live watermark with the viewer's own email, partially masked (jo•••@example.com). It moves, so it can't be covered with a rectangle.
What this solves
It kills casual sharing: whoever screen-records and reposts is distributing a video with their own identity burned into it.
What this does NOT solve
No video protection on the web stops a camera pointed at a screen. Anyone promising that is selling something that doesn't exist. What the watermark does is make a leak traceable — and that's what changes behaviour.
Does the full email show?
No. It's masked on the server before it ever reaches the player, precisely so a screenshot doesn't expose a student's full address.