Ava DuVernay on significance of August 28 in black history
From Emmett Till's death to President Obama's acceptance of the Democratic presidential nomination, August 28 throughout the years has been a significant date in African-American history. Director Ava DuVernay, who made the orientation film for the Smithsonian's National Museum of African American History and Culture, tells Gayle King why she decided to create the film around the historical date.