I've always been taught that whenever someone has a gun pointed at you, you do what they tell you to do. If you know without a shadow of a doubt that they are going to pull the trigger and kill you, then sure, go for broke. Otherwise, keep your hands in plain sight, shut up, do what you're told, and bide your time until a gun is not pointed at you to fight back.
The video, IMO, is a load. The really huge guy holding the gun against the teeny tiny guy does nothing but act like he's getting hurt while the little bitty dude fumbles with the gun.
Call me crazy, but if a guy that size is pissed enough to hold a gun to my head, I'm pretty sure he's going to do more than stagger backward after I grab for his gun and do some "judo-chop", a la James Bond, against his chest.