“20,000 Days on Earth,” Cave’s new documentary film (co-written with the directors Iain Forsyth and Jane Pollard), chronicles a day in this life, the 20,000th to be exact. It’s a very full day, partially staged, with time to write music, see his therapist, drive leisurely around in the Brighton mizzle, lunch with Warren Ellis of The Bad Seeds, spend an hour or two in his archives, likewise in the studio, eat pizza and catch a spaghetti western with his kids, and front a show. The film builds like a song. From wisps and scraps of dreams it finds flesh with collaborators, shape in the studio, and catharsis before the crowd’s enraptured eyes. It’s a patient, funny, interesting film about what might be one of the most fully actualized lives currently being led. And without ever patronizing or ringing false, it presses home the way that this actualization follows from dissatisfaction, from desire chased but never caught.