In this article, it talks about how the police went to close down a freestyle rap session in downtown Memphis. When a concert attendee started to film the police, an officer took his phone, and threw him in a squad car. Everyone has the right to videotape police activity.
This page is one-sided. It doesn't look at the perspective of the police. Maybe there were noise complaints, so the police had to put an end to it. That doesn't mean it isn't happening though.