> when an embedded video loads for me, youtube still knows that it's me
If/when third party cookie blocking is fully deployed, this won't be true. Your browser won't send YouTube's session cookie to YouTube when it's loaded in an iframe on an unrelated site, so YouTube won't know you're a premium user.
If/when third party cookie blocking is fully deployed, this won't be true. Your browser won't send YouTube's session cookie to YouTube when it's loaded in an iframe on an unrelated site, so YouTube won't know you're a premium user.