John Carney’s cult favorite Once (2006) took a thin love story and filled it out with magical scenes of musical improvisation and discovery; this follow-up works the same way, its soft-rock bonhomie prevailing over a story that often registers as trite or naive. A British songwriter (Keira Knightley) accompanies her musical and romantic partner to New York City, where he’s been signed to a major label; after he dumps her for someone else, she’s adopted by a down-and-out A&R man (Mark Ruffalo), who assembles a band around her and records them live on the city streets. The stars work overtime to put this across—particularly Ruffalo, who’s saddled with a corny subplot involving the record man’s alienated teenage daughter (Hailee Steinfeld of True Grit). Much of the story is resolved in a hurried closing-credits montage, which suggests the narrative kept getting elbowed out by the more satisfying musical segments. With Catherine Keener, Mos Def, and CeeLo Green.