After Inside Llewyn Davis, here's Outside Keira Knightley. John Carney's latest tale of random hearts brought together by song may not have the rough-and-ready brilliance of Once (or a tune to match Glen Hansard and Markéta Irglová's Oscar winning Falling Slowly) but it does a surprisingly good job of making us believe in the slightly preposterous idea of KK recording an album on the streets of New York.

Knightley plays Greta, a singer-songwriter stumbling from a recently stalled relationship with a corporate sell-out rocker (Maroon 5's Adam Levine), who catches the drunken eye/ear of washed-up A&R man Dan (a typically ruffled Mark Ruffalo). Hearing in her hesitant open-mic strummings the makings of a full-blown hit (Carney brilliantly revisits the opening downbeat performance to dramatise an imaginary upbeat orchestration), Dan attempts to sign Greta to the label from which he has recently been dumped. But when her indie integrity reawakens his own long-lost musical passion, the odd couple embark on a series of makeshift pavement and rooftop recording sessions in which the natural sounds of NYC (sirens, trash cans, car-horns) become an integral part of the endearingly skiffled songs.

With original music co-written by New Radicals frontman Gregg Alexander (the songs are serviceable, if not spine-tingling), Carney's bigger-than-before budget feature still retains a distinctively ramshackle charm. Knightley and Ruffalo are nicely natural as the increasingly idealistic musos who discover that a song can save your life, their streetwise story mutating into an anti-establishment fairytale with added exhaust fumes. I found it moving, funny and really rather charming, provoking more than enough laughter and tears to dispel my underlying anxieties about the "live" performances.