Co-produced by Danny Glover, the film has been traveling the festival circuit this year and just opened in NYC last week. Read the NY Times review here.

Unknown children playing in the street in Harlem, New York in 1974, an image from The Black Power Mixtape 1967-1975, directed by Göran Olsson. (Photo: Anders Ribbsjö/IFC Films)
There is an interesting audio interview with the producers at TheWorld.com which talks about the outsider perspective contained in the footage, and even has some comments from the original filmmakers.
Additionally, there is an exhibition of stills from the film happening now at thirdstreaming in NYC.