Power Ballad      Director: John CarneyCert: 15AStarring: Paul Rudd, Nick Jonas, Peter McDonald, Marcella Plunkett, Havana Rose Liu, Jack Reynor, Beth FallonRunning Time: 1 hr 34 minsStick with me here. I am going to compare the films of John Carney to the albums of Van Morrison. A musical analogy seems, after all, appropriate for a film-maker much concerned with the way the popular song can access unprocessed emotion. Just as Morrison spent decades delivering albums that seemed superficially similar but always hit fresh melodies, Carney has hit upon a happy formula that rarely fails to generate warmth and charm.Power Ballad, the director’s ninth film, is no sort of Saint Dominic’s Preview, but it might (stay with me, Vannies) be a Poetic Champions Compose. Making good use of Paul Rudd and returning members of his stock company, Carney gives us a solid slab of his diegetic musical shtick that shifts into something more memorable in its euphorically pitched denouement.We know that Rick Power (we’ll get to the names in a moment) is a decent guy, as he’s played by the perennially agreeable Rudd. Once a budding pop star, he settled in Dublin after the dream died and now plays in a wedding band cheesily titled Bride and Groove. Rick slips in the odd tune from Octagon, his earlier group, but for the most part he plays covers of the usual ballads. Peter McDonald, who also co-wrote, plays Sandy, a bandmate. The Carney recidivists Marcella Plunkett and Jack Reynor make their welcome returns as, respectively, tolerant wife and back-slappy manager.The plot hinges on Rick’s encounter, at one of his nuptial gigs, with a struggling superstar played by Nick Jonas. Carney and McDonald have named him Danny Wilson in honour of, presumably, the Scottish group behind the delightful 1987 hit Mary’s Prayer and, by a further remove, Meet Danny Wilson, the Frank Sinatra film that inspired that band. Rick’s daughter, played by the excellent newcomer Beth Fallon, is named Aja, an unmistakable reference to Steely Dan’s greatest album. So, yes, there is fun here for all middle-aged rock fans and cryptic-crossword enthusiasts.Where were we? After the wedding, Rick and Danny retire to a quiet place and bond while jamming their way through their own compositions. You know the Carney vibe. Hunched intensity over acoustic guitars and all that. The party breaks up. Our hero returns to his charming family. Danny retreats to his mansion and plucks away at a number titled How to Write a Song (Without You). It becomes a huge hit. His career is revived.But wait. One day Rick is wandering through the shopping centre – is that Dundrum? – when he hears the tune drifting across the concourse and recognises it as his own. Of course, he has no way of proving that. He is now wedding-band David against pop-star Goliath. No Los Angeles lawyers will take him seriously.[ Paul Rudd on filming in Dublin: ‘The people here are so hilarious. It was kind of a hoot’Opens in new window ]The film has some trouble finding things to do in its third quarter. Sandy and Rick head to the United States, where they career from mad pleading to farcical bumble. We end up pretty much where we were, before lunging towards that satisfactory close. The director has perfected his technique over such fine predecessors as Once, Begin Again (criminally underrated) and Sing Street. Once again, the individual elements are nicely honed. If anyone else but Rudd played this lead, few would put up with his dad-head crises. The song at the centre is, impressively, just about convincing as a potential smash even if the precise nature of Jonas’s stardom feels a tad ill-defined. What keeps Power Ballad flowing is the juice of the dialogue, the comic humanity of the plotting and, above anything else, that charmingly ingenuous belief in pop music as something that truly matters. Good work.In cinemas from Friday, May 29th