<human>: Came home to dude being arrested a block away. No mistake about it, he was resisting the officers on scene. A couple people already had their cameras rolling from a distance, so I wasn't filming yet. Everything was fine until we saw an officer raining knees down on his head when he was well under control already. 

At that point people started running towards the scene to get it on film. I made the mistake of saying 'you should know you're on film'. Then officers tried to confiscate my phone as 'evidence' that he was resisting. If I would have caught the knees on camera I wouldn't have a phone and that 'evidence' would be destroyed. 

At least me telling them they were on camera stopped those knees REAL quick. If they were truly warranted the cop wouldn't have stopped doing them immediately after I said it.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: When filming cops, get it on film, be quiet, and walk away before they can confiscate your 'evidence'. Because they WILL try to take it..