To recap, the Pixels plot centers around aliens who discover video footage of classic arcade games. After seeing them, the aliens believe Earth is preparing to wage war - you might too if you were an extraterrestrial who stumbled upon Space Invaders. The aliens invade Earth, using the games they've seen as templates for their attack. Of course, it's up to some "old-school arcaders" to defeat the aliens, save the day, and try not to be portrayed too nerdily.
If the plot and name sounds familiar, it's because you've probably seen it as Patrick Jean's excellent short film from a few years back; and the movie is based on Jean's video. It seems following the success of Wreck-It Ralph, 1980s gaming is in when it comes to films; Sony Pictures said Columbus and the studio are working with "many of the 1980s' most iconic video game brands" to bring together characters from arcade classics on the silver screen.