The historically momentous 1974 Rumble in the Jungle between Muhammad Ali and George Foreman got the movie it deserved in 1996, with the Oscar-lauded documentary When We Were Kings. Now one of the film’s editors, Jeffrey Levy-Hinte, has used its outtakes for an essential film about Zaire ’74, the rollicking, politically magnanimous three-day festival of music that was the fight’s opening act. Talent on hand included James Brown, Celia Cruz and the Fania All-Stars, B.B. King, Miriam Makeba, the Spinners, and Bill Withers. It must have been a simpler time: Broad-minded cinéma vérité prevailed in the creation of nonfiction films, and hope trumped cynicism in racial politics. The sound of black power was alive and righteous, yet so funky, so sweet. Dependably photographed by Albert Maysles, Paul Goldsmith, Kevin Keating, and Roderick Young, Soul Power is sort of its own little master class on looking and listening.