Tough. Cops should wear recorders and bystanders should be able to record anything they see. Transparency is a virtue.
The cops in my city have car cams and body cams, and seem to be OK with it.
There’s a good story of the guy who took a traffic ticket to court, claiming the cop was being very disrespectful to the citizen. Apparently the guy’s demeanor changed greatly when the cop said “Your honor, I’d like to offer this body cam video as evidence.” The video showed who was disrespectful to whom, and it wasn’t the cop misbehaving.
The problem with these videos is that people don’t start recording them until they notice something is “happening.” What led up to the “something” in the time before the witness took notice of it, got his phone out and started recording is never clear.