Okay imagine your filming the interrogation room scene with Joker and Bats. We start off with an OTS (over the shoulder) shot from Joker to Bats. The same shot where he says "You wanted me? Here I am." Okay, that side we're shoot on, we've established an imaginary 180 degree line. We can move the camera anywhere on this line, switching focus from Batman to Joker. But we can not cross this line, because when the camera cuts back to another character their line of sight as been shifted and seems off.
So in the trailer, Batman is looking camera right. If they had stayed on the line with Joker, Joker should be looking camera left, so that the two seem like they are looking at each other. Instead, in the trailer, Joker is looking camera right. The same direction as Batman. If this wasn't a trailer and the scene played out as so, it would knock off your viewing of the scene and wouldn't feel right.
The only way you can motivate to the other side of this line is if you move the camera over there while filming.