Musicians and partners Glen Hansard and Markéta Irglová won the hearts of moviegoers (and Oscar-watchers) with their performances in the 2007 indie hit Once, which also netted them an Academy Award for their song “Falling Slowly.” They were a fascinating pair: He was a brooding, thirtysomething Irish folkie, she was a 19-year-old emo Czech girl with a lovely voice. Together they made beautiful, unassuming music that seemed to reflect (in its typically understated way) their own quiet romance. The lovely documentary The Swell Season, which premieres tonight at the Tribeca Film Festival, follows the duo and their bandmates on the road as they meet their public. The film begins to show the slow tears in the fabric of Hansard and Irglová’s relationship — both with each other and with their newfound public identities. Irglová doesn’t know if she’s ready for this level of stardom. Hansard, for his part, isn’t sure he even wants this level of mainstream acceptance; he bristles at his working-class mother’s pride at the Oscar win. What begins as something like a concert documentary winds up becoming the mirror opposite of Once: a quiet, stark portrait of how a relationship falls apart. In this clip from the film, we see Irglová and Hansard during an intimate practice session, while she explains how she first fell in love with him.