Tribeca Audience Prize winner “United Skates” treats you to a dazzling display of roller skating styles in black communities across America. For several generations, roller rinks provided a place for skaters to come together in harmonious movement. Now that tradition is threatened by rinks closing throughout the country. Cities are more likely to give tax breaks to corporate stores than to havens of black culture. Filmmakers Tina Brown and Dyana Winkler spent several years documenting the trend of rink closures and the activist skaters fighting to keep them open. Host Thom Powers interviews Tina Brown and skater Reggie Brown (no relation). The conversation took place in front of a live audience at Pure Nonfiction at IFC Center in New York City. “United Skates” will be available on HBO starting February 18.