The entire MV is a single long take, unedited, with each person singing only one line throughout the song. I lost count of the number of actors (there were too many!), and each had their own style of "fake-singing". Then they magically all end up in a classroom at the end. I can't even imagine how many times they rehearsed... They're so talented!
Apparently, it was made by a group of German college students. For more information, you can check out their official lip-sync organization website at universitylipdub.com.