https://www.cnet.com/news/avengers-infinity-war-trailer-justice-league-reacts-marvel-dc/

"There's something we need to talk about, and I don't think that you're going to like it," says Commissioner Gordon (J.K. Simmons) as the DC heroes gather and then watch the preview. From then on out, young Flash (Ezra Miller) steals the show, as he nervously watches Thanos appear invincible against Earth's Mightiest Heroes.

YouTuber DrMachakil posted this video and also the reverse version back in March, showing the Avengers assembling to watch the League go to work. You've always gotta keep an eye on the competition, after all.