Did I just hear someone say "I'm sorry" with thick american accent at 0:11 ??
And I agree with others, it is ridiculous how close people can get to this facility and observe it. And what's stopping foreign spy from taking measurements on the J-20?
I mean, the J-20 flew so close literally just meters above the spectator's head, someone could probably just measure J-20's radar reflectance with a hand-held radar!
Okay maybe quite a bit of exaggeration, but I am sure CIA/DIA (Defence Intelligence Agency) probably had some people on the ground with miniturized high tech radar disguise as a camera and record all the preliminary measurements.