Since the late 90s, Jack Black has teamed with Kyle Gass in the comedy-rock duo Tenacious D, and their short-lived HBO series led to Black’s breakout role in High Fidelity. Now that he’s a movie star, Black has invested some of his capital in this big-screen outing, though the format magnifies the disparity between the two performers. Black’s love of heavy-metal pomp animates the giddy opening sequence, a rock opera with cameos by Meat Loaf and Ronnie James Dio, and a few choice gags pop up later (asleep on a park bench, Black is menaced by Alex and his droogs from A Clockwork Orange). But most of the movie, about the search for a magical guitar pick, farts along at the level of a “Wayne’s World” sketch. Liam Lynch (Sarah Silverman: Jesus Is Magic) directed. R, 97 min.