Filmmaker Yael Hersonski, discusses “A Film Unfinished:” her acclaimed documentary about the atrocities in The Warsaw Ghetto during World War II. The footage, shot by the Nazis in May 1942, became a resource for historians. However, the later discovery of a long-missing reel that included multiple takes with staged scenes, complicated earlier readings of the footage. “A Film Unfinished” presents the raw footage in its entirety, carefully noting fictionalized sequences, and explores the making of an infamous Nazi propaganda film. The film opens in New York August 18 at Film Forum and at Lincoln Plaza Cinema.