Concert films follow a pattern. The star sings the hits, intercut with breathless fans and reflective interviews. Rare is the music doc that captures a moment as poignant as one towards the end of this film about Katy Perry, the popster who had a strict religious upbringing in California. She says all she ever wanted was to be on stage in a glittery costume with thousands of people singing along. This wish is granted as she sings her infectious pop peppermint drops to adoring hordes during her yearlong tour. Katy twirls in her tarty Candy Land costumes on stage, as her marriage to Russell Brand begins to splinter off the stage. Reality TV producers Dan Cutforth and Jane Lipsitz assembled 300 hours of already shot footage into a compelling rock doc narrative with a bittersweet coda.