POSITIVELY 4TH STREET: In creating the soundtrack for their folk-era film Inside Llewyn Davis, the Coen brothers and T Bone Burnett turned to present-day folk hero Marcus Mumford, who’s credited as associate producer on the project. The 14-song collection (Nonesuch, 9/17) will feature songs by folk legends such as Dave Van Ronk and Bob Dylan along with musical covers performed by cast members Oscar Isaac, Carey Mulligan (Mumford’s significant other), Justin Timberlake and Mumford himself, who also landed a part in the film. Check out the latest trailer, and go here to listen to Isaac and Mumford perform the Van Ronk-associated “Dink’s Song” at Caffe Vivaldi in the Village. (7/3a)