Your premise is sound, though the rioters will probably still upload through apps like Periscope, etc.
Unless cell phone start getting jammed in that area?
The police have the ability to shut down cell service in an area. I would not be surprised if the Feds have the ability to get a list of all cell phones within an area, and order them shadow banned from social media, so the video doesn't show up, or remotely wipe their phones.