This appears to be professionally shot B-roll from the set of Kimberly Peirce's new Carrie remake, showing Chloe Moretz in character, during a take. You'll also see Gabriella Wilde as the new Sue Snell, and some of the other cast as they act out a bit of that high school bullying we all love so much.
Interesting that Steve Yedlin is shooting this. He also shot May and Brick, both of which share some of the basic elements of Carrie, not to mention the upcoming, and rather handsome looking Looper.
Thanks to BD for the embed.