R&B singer Chris Brown is reportedly down to give police the blow-by-blow details for what happened Sunday (January 27) night in his publicized altercation with Odd Future's Frank Ocean.

What's more ... sources say his attorney Mark Geragos' team has surveillance video of the last part of the fight, and Chris is as clean as a whistle -- not throwing a single punch. But here's the thing.  We're told the video also clears Frank Ocean -- he never takes a swing at anyone.  The fighting is between the two posses. The video, however, is not the be-all and end-all, because it only captured the back end of the fight.  The altercation began in the parking lot and no cameras were trained on the action.  So it doesn't show who started it.  The fight moved into the lobby, and that's where the camera captured the brawl. (TMZ)