It's hard to believe it's taken 35 years for images this vibrant, this joyous, and this era-defining to reach the big screen. Yet that's the gestation period for Soul Power, the concert film that finally brings to life the three-day music festival known as Zaire '74, which was intended to accompany the "Rumble in the Jungle" boxing match between Muhammad Ali and George Foreman (before a busted lip prompted Foreman to postpone by six weeks). The reason for the film's delay is clear, however -- its very existence was a direct response to how much footage wasn't considered germane to When We Were Kings, Leon Gast's 1996 documentary about the fight, which itself was delayed by legal disputes involving the project's original Liberian financiers. Jeffrey Levy-Hinte, an editor on that Oscar-winning film, was inspired to rescue the hours of unused concert footage from the vaults, and the end result is Soul Power. Fans of both movies and music should be thankful he did. Like so many concert films that have come before, Soul Power takes the viewer all the way from erecting the stage through the final bows. But what's so different from those films is the veritable melting pot of musical creativity on display here. The festival was conceived as blending the best African-American musicians and the best African musicians, but those loose guidelines had no problem embracing such performers as Cuba's Celia Cruz and her salsa supergroup, the Fania All-Stars. The viewer gets an idea what's in store from a jubilant airborne jam session, which for all we can tell lasted from start to finish of the 13-hour flight from Paris to Kinshasa -- and which seems like one condensed encapsulation of the spirit of the 1960s. The musicians who disembark on the other side are a who's who of 1970s R&B: James Brown, B.B. King, Bill Withers, the Spinners. Seeing these acts in their prime is one thing; watching them interact with other personalities -- such as Ali and fight promoter Don King, who deliver some rich sound bites on race and contemporary life -- is another. Levy-Hinte was wise not to construct Soul Power as just a string of musical performances. The camaraderie of the performers, the promoters' logistical headaches, the anticipatory glee of the locals, and other on-the-ground details turn out to be indispensable ingredients. On the whole, it's a glorious teleportation into a time long past, and Levy-Hinte keeps it that way by resisting the temptation to contextualize the festival via 21st century interviews with participants. Modern reflections would have broken the spell of the footage that Kings director Gast and crew shot at the time. When the curtain does drop on opening night, Levy-Hinte actually leaves his viewers wanting more. Each musical luminary is given one song -- in some cases, only part of one song -- to strut his, her, or their stuff, in keeping with the director's balanced approach. But the selections are dynamite. Viewers will cherish every facial contortion in B.B. King's guitar solo, every note held for impossible lengths by a crooning Bill Withers, every drop of sweat off the brow of James Brown at his most gymnastic. For every familiar act, though, there's a genius African counterpart who may be brand-new to Soul Power's audience. Most memorable among these is Miriam Makeba, whose "Click Song" demonstrates her fitness with that inimitable consonant sound common in tribal languages. Language could have been a significant barrier during Zaire '74, as the most famous performers spoke and sung in English, while the audience was largely French-speaking. Well, the international language of music triumphed back then -- so should it now in making Soul Power an international hit.