VIDEO : U.S. Rapper Common Talks Teaming Up With Ava Duvernay

Rapper Common said it was "very special" to team up again with director Ava DuVernay on her latest documentary "13TH." The film argues that slavery is still alive in the form of mass incarceration that disproportionately affects black people, even though slavery was officially abolished in the United States 150 years ago. Common released his eleventh album called "Black America Again," back in November, and the song "Letter to the Free" was used in DuVernay's documentary.