From Rollingstone.com:
Film features previously unseen footage of Sly and the Family Stone, Nina Simone, Stevie Wonder, and more performing at “Black Woodstock” festival in 1969

Questlove’s documentary, Summer of Soul […Or, When the Revolution Could Not Be Televised], will arrive in theaters and on Hulu on July 2nd.
The Roots drummer’s directorial debut delves into the little-known history of the Harlem Cultural Festival, dubbed “the Black Woodstock,” which took place the same summer as Woodstock in 1969 over the course of six weeks at Harlem’s Mount Morris Park [now Marcus Garvey Park]. The lineup for those shows featured Sly and the Family Stone, Nina Simone, B.B. King, Gladys Knight and the Pips, Stevie Wonder, and more, and Summer of Soul features never-before-seen footage from those concerts.
Summer of Soul had its world premiere at the Sundance Film Festival in February. It was awarded both the U.S. Grand Jury Prize and the Audience Award in the U.S. Documentary category. “It has always been a dream of mine to direct films and telling this story has truly been an amazing experience,” Questlove said in a statement at the time. “I am overwhelmed and honored by the reception the film is receiving.”

Not long after Summer of Soul’s success at Sundance, it was announced that Questlove will direct an as-yet-untitled documentary about Sly Stone.