SANCTUM ★★

(Cinemax on Comcast) This Australian adventure-survival saga, “presented by” executive producer James Cameron as a way to keep his 3-D equipment from gathering dust between “Avatar” installments, is a B-movie down to the bare-bones plot and boilerplate dialogue. The 3-D camerawork provides more depth than the 2-D characters, but the trapped-in-a-cave suspense has its moments. (R; runs through Sept. 27)

BLACK SWAN ★★★

(HBO on Comcast) Natalie Portman speeds around Darren Aronofsky’s commercially daring freak-out in a state of corseted frenzy. She tries to save her starring role in “Swan Lake’’ from the company’s sexy new dancer (Mila Kunis). The film really works as a study of artistic obsession, as a psychological horror-thriller. The dancer’s paranoia and narcissism overtake her. Is she dreaming or displacing? Aronofsky is very good playing the ambiguity. With Vincent Cassel, Barbara Hershey, and Winona Ryder. (R; runs through Oct. 1)

THE DISCREET CHARM OF THE BOURGEOISIE ★★★★

(Showtime on Comcast) Luis Bunuel’s surreal evaluation of the grossness of the middle-class, elusive but powerful. (PG; runs through Sept. 30)