Martin Mull used to talk about “the folk-music scare” of the 1960s: “Boy, that was close, wasn’t it? That crap almost caught on.” This mockumentary from director Christopher Guest (written by him and Eugene Levy) catches both sides of the quip: We see why the music was “crap,” but we also see why it almost caught on. The premise is a reunion concert of three 1960s groups: the male trio the Folksmen, the white-bread ensemble the New Main Street Singers and former folkie sweethearts Mitch and Mickey (older viewers will know at once the real-life inspirations for these parodies). The film deftly mixes equal parts of hilarity, poignancy and lively hootenanny gusto. If the Academy didn’t take itself so seriously, Eugene Levy (as the mentally unstable Mitch) would be a front-runner for one of next year’s Oscars.