(me guessing)
Chief must have gotten his Promethean vision right after he and Cortana landed. However notice at the end of the trailer Cortana activates it and he does not. Also notice that the unsc is about to get taken captive before it lands. So does that mean that game footage is somewhere near the middle or beginning of Halo 4? Because apparently he has already landed too. So anyway both the chief and the infinity get taken captive only time will tell if the same happens to the covenant, but wait what about the Promethean vision, exactly, Chief must have got it right after he landed or sometime after that too, but not when he seen the infinity coming toward him. So that being said that trailer would land you right in the middle of the game that is Halo 4. The only way out is through the forerunner can chief fight his way out or does get knocked out? Exactly. Take a look at his shields, they are down. So that would mean he is taken captive. Cortana helped him get his Promethean vision.
There are also blue forerunner and orange forerunner…hm. Why? Cortana, might have something to do with that or not. I seen that to so I’m just wondering.