I looked up the "Periscope" smartphone app. It allows you to broadcast video in real time on twitter. This looks like JUST THE APP for people to have on their phones, in case they come across misbehaving public employees.
In case they try to confiscate your phone to suppress being recorded, you can just tell them, "Sorry, this video is already currently being sent out LIVE on twitter, including your attempt to violate my rights. SMILE m----f---er!"
"Sorry, this video is already currently being sent out LIVE on twitter,....would you like to introduce yourself?