Who is the "we" in Bert Marcus and Cyrus Saidi's What We Started? This look at electronic dance music speaks of the genre's origins — in Manhattan disco, Detroit techno, etc. — in the third person, and incompletely; the interviewees we do hear from are mostly those who rode predecessors' coattails to fame and fortune. Nevertheless, the throbbing documentary tells enough of the story to show today's legion of David Guetta fans where he and his peers came from. Viewers who suspect this scene's superstars will be in 20 (or 10) years will likely remain unconvinced when the credits roll.