David Hockney once said, “It is very good advice to believe only what an artist does, rather than what he says about his work.” On that note, providing insight into what Hockney does is the goal of Exhibition on Screen, a documentary featuring two of his blockbuster exhibitions at the Royal Academy of Arts—”A Bigger Picture” (2012) and “82 Portraits and One Still-Life” (2016). Combined, they attracted 750,000 visitors. In this walk-through, Tim Marlow, the Royal Academy’s director of artistic programs, examines the nuances at the heart of Hockney’s art. —E.C.