In October 1971, Pink Floyd gave a spectacular concert to an audience of thousands of ghosts in the volcanically ravaged ruins of Pompeii. Alone in a stone amphitheater (save for the production crew), the prog gods crank out “Echoes,” “Saucerful of Secrets,” “Set the Controls for the Heart of the Sun,” and more, captured with slowly circling cameras, totemic framing, and even the occasional split screen. Featuring interview snippets covering the recording of The Dark Side of the Moon, the state of the music industry, and oysters.