The long-running TV dance program Soul Train was so punchy, colorful, and buoyant that no documentary maker with an ample supply of clips could possibly go wrong. Launched in 1970 on Chicago’s own WCIU, the show quickly moved out to Los Angeles and went national, becoming a cultural touchstone for blacks and a bracing antidote to the white domination of network TV. (A damning clip from American Bandstand shows Dick Clark referring to “Gladys Pips and the Knights.”) Video maker J. Kevin Swain includes talking-head commentary from Aretha Franklin, Patti LaBelle, Rosie Perez, and others who appeared on Soul Train, but the key figure is host Don Cornelius, the suave south-sider who created the show and, poignantly, struggled to stay current as soul gave way to disco and hip-hop. The performance clips are woefully short but feature such greats as Stevie Wonder, Curtis Mayfield, Marvin Gaye, and Sly Stone.