The “Rumble in the Jungle,” the historic 1974 heavyweight match between George Foreman and Muhammad Ali in Zaire, was preceded by a weekend music festival with such stellar talents as James Brown, B.B. King, Bill Withers, Miriam Makeba, the Spinners, and Celia Cruz and the Fania All-Stars. This concert documentary, assembled by Jeffrey Levy-Hinte from the same trove of footage that produced Leon Gast’s When We Were Kings (1996), taps into the same swell of African and African-American pride (though the fight was actually postponed after Foreman was injured in training, and took place six weeks after the show). The logistical buildup to the festival is routine, and when it finally begins, Levy-Hinte doles out a disappointing one song per artist. But the movie catches James Brown at the height of his funk fever and “I am somebody” empowerment; he stands as the musical counterpart to Ali and a genuine American hero.