Two documentaries use the form in very different ways -- one far-ranging, the other intimate. ''Amandla! A Revolution in Four-Part Harmony'' (PG-13, 103 mins., 2002, Artisan) charts the pivotal role of protest music in black South Africans' struggle against apartheid using interviews with activists, political exiles, and even former riot police, plus, always, the music -- at turns cheerful, defiant, and mournful. ''Blind Spot: Hitler's Secretary'' (PG, 87 mins., 2002, Sony Pictures Classics), meanwhile, has a woman simply facing the camera to, well, face her past; recounting memories both banal and chilling, she ultimately must ask herself if being ''unaware'' made her any less culpable. The films couldn't be less alike: The first -- the title means ''power'' in Xhosa -- offers an awe-inspiring revolution in which music was a weapon of intimidation, resistance, and hope; the second, an extremely personal meditation on guilt. But both illustrate the documentary form's ability to make history vivid. EXTRAS Amandla!: A Q&A with the filmmakers, their commentary, and a brief chat with South African pop star Dave Matthews are less compelling than the additional interview footage and a spine-tingling concert by activist musician Vusi ''The Voice'' Mahlasela. A- Hitler's Secretary: None.