The Punch Brothers, Marcus Mumford sing "The Auld Triangle"

The Punch Brothers - Chris Thile, Gabe Witcher, Noam Pikelny, Chris Eldridge and Paul Kowert - join with Marcus Mumford to perform "The Auld Triangle," at New York's Town Hall, in an excerpt from the Showtime documentary, "Another Day/Another Time: The Music of 'Inside Llewyn Davis,'" celebrating the folk music of the Coen Brothers movie.