Such sites have so far been able to avail of 'safe harbor' exemptions in the US that mean they are not culpable for user-generated uploads that have unlicensed content such as music. In Europe, the 'mere conduit' clause offers similar protection for services.

They do, of course, respond to takedown notices from rights holders if they identify a video that breaches copyright. The difficult in policing this properly is the sheer volume of user-generated uploads that happen on a site ...