On the Sailgroove website Patrick Rynne has put up a couple of videos where you can be the protest-committee and the umpire.
See the action on the water and decide for yourselves.
He's done this by filming two Optimist in different situations:
You make the Call - Episode 1 is about a windward mark rounding
You make the Call - Episode 2 is about a classic slam dunk situation.
In the first situation the 'testimony' of the sailors is included. As if you see this video in the protest-room, because one of them has brought it with them. So in that one you are allowed to see the video as many times as you please, getting to what actually happened. Please remember the restrictions a camera has - specially in depth perception.
In the second situation you have to take the decision as an umpire, on the spot. Well okay, you can see the video twice and then make a decision.
Good practice, but also a reminder that videos will never replace on the spot observation.