Once again, Irish writer-director John Carney delivers an aspartame rush of enjoyment with this terrific comedy of bromance and betrayal in the world of music, starring Nick Jonas (from the Jonas Brothers) as Danny Wilson, a preeningly insecure ex-boyband superstar trying to go solo and searching for a hit single, and Paul Rudd as Rick Power, a washed up wedding-singer who rashly plays Danny a catchy song he’s been working on.

Power Ballad is about making it and dreaming big, about every busker never giving up on hopes of one day being mega. But as so often with Carney, it’s about something else, usually left unacknowledged in movies about music or any sort of showbusiness: the terrible binary of success and failure. For every star there is an invisible army of losers, the sad cases who used to be the star’s home town friends or early collaborators and have a lifelong task ahead of them coming to terms with not making it. In the bitter words of Les McQueen, rhythm guitarist for failed 70s group Crème Brulee on TV’s The League of Gentlemen: “It’s a shit business …”

Rudd’s Rick is a likable American guy who used to be in an up-and-coming 90s US band, and Carney pastiches some analogue interview footage of Rudd looking younger back in the day with long hair, eyeliner and a Bill Hicks T-shirt. Not that this Dorian Gray performer needs any kind of fakery. But Rick fell in love with a wonderful Irish woman Rachel (Marcella Plunkett) while playing Dublin, stayed with her in Ireland, and now they have a teen daughter called Aja (Beth Fallon) who is the apple of his eye; she tells him girls aren’t interested in “love” in songs any more, actually it’s “revenge”. An interesting omen.

Rick is more or less resigned to playing mainstream covers in a wedding band, but secretly tormented with regret for having sabotaged his career. One night, they play a wedding reception at a fancy country-house hotel and Rick resentfully clocks the fact that Danny Wilson is one of the guests; but he can’t help being flattered in his beta-male submissive way when Danny asks to join them on stage and they crush a version of Stevie Wonder’s I Wish. Poor Rick hangs out with Danny afterwards in his palatial suite, drinking, smoking weed and jamming, and he plays for Danny a really sweet song he’s proud of and they tinker with it. It is a brilliant moment later when, depressed while shopping, Rick hears a weirdly familiar hit pop song echoing around the mall, supercharged with LA production values; Rudd cleverly conveys Rick’s discombobulated fear that he’s hallucinating, and then his sickening realisation.

Only Carney, that music-movie connoisseur, could have created that extended setpiece scene showing Danny and Rick creatively hanging out and working on the song and stayed with the scene at such extraordinary length, taking the compositional process so seriously. Richard Curtis would have dispatched it in 45 seconds – although this did remind me a little of Curtis’s amiable and underrated comedy Yesterday, about the goofy dope in an alternative universe who passes off Beatles songs as his own. In Power Ballad, the toxicity of masculinity is sweetly redeemed.