The opening scene of the new Irish film Once (released nationally on 30 August) is an extended long shot of a busker standing on a Dublin street, strumming his guitar and belting his lungs out. A junkie loiters edgily. He's not going to steal the busker's meagre stash of coins, is he? He is indeed. The long shot, the passers-by and the lighting lend the sequence a documentary feel, and by the time we see a close-up it has become entrancing. The busker's face is refreshingly haggard and non-Hollywood: this is The Guy (Glen Hansard), who is to be the main character. The eventual snatch-and-grab and the perfunctory chase that ensues make for a very funny scene. The junkie will disappear, but the battered warmth of The Guy (no other names are given for him, or for the other protagonist of the story, The Girl) will remain and, in its low-key and disarming way, spread through the film.

The Guy gives a little help to his dad (a beautifully understated performance from Bill Hodnett) in his run-down vacuum-cleaner repair shop, but really he lives for the music. As musicians go, he seems at first to be in the lower half of the barrel. He's got a fine voice and an arresting intensity, but then so do a lot of buskers. We pass them in the street with barely a thought; they seem grubby members of an underclass. His girlfriend, whom we never meet, has left him and gone to London. It's not clear whether this is a trial separation or the end of the affair, but The Guy seems to retain a guarded, if melancholy, optimism about the situation.

The Girl (as distinct from that off-screen girlfriend), played by Marketa Irglova, is a recent arrival from the Czech Republic: a musician over there, but in Dublin she's selling The Big Issue on the street and, in restaurants, those cellophane-wrapped long-stemmed roses. She's blunt, curious, forward. There's a quality in the dishevelled busker that intrigues her - and in her that intrigues him.

 If you haven't guessed it already, there's something of the fairytale about all this. The film's director, John Carney, was in the Irish band The Frames, as was Hansard. Irglova is a real musician too, and had collaborated with Hansard. The story was developed for these two and, though they are amateur actors, their acting is not amateur, despite the occasional rough moment. You forgive the minor faults, and slowly this charming yet slender film grows on you.

It's odd to call Once a musical - Chicago it ain't - but in its own gently genre-breaking way that's exactly what it is. The drama is played out, and built, through music; Hansard and Carney wrote some of the songs with scenes in mind. These are placed naturalistically - in a piano shop, a recording studio, even on the back of a bus - never compromising the heavily realist setting, and they tell the story of a one-week blossoming of love against a background of getting enough money to record a demo.

The film has been shot with a grainy hand-held camera, recalling the Dogme edict. It has a rough, boisterous energy reminiscent of Alan Parker's The Commitments (1991), from the Roddy Doyle novel, a film in which Hansard had a small role as one of the guitarists. And it's full of a lilting low-key humour, as when, at the back of that bus, in answer to The Girl's question about what happened to the ex-girlfriend, The Guy pulls out his guitar and ad-libs spontaneous lyrics about  "a broken-hearted hoover-fixer sucker guy".

In a sense everything that happens to these two is unlikely. They negotiate a price on the recording studio, then go and get the loan; their producer, who comes with the studio rental, is disdainful at first, and only half-listening. Then - of course - his ears prick up and he comes around. And so on. A subtle ending goes against the expectations that have been created, but caps off the film in the manner of a Russian short story.

Closer to home, Tony Ayres' The Home Song Stories (released nationally on 23 August) is also genre-bending, in that it looks like a fictional feature but is very much an intimate autobiography; it is even capped off by a montage of old black-and-white photos of the real people with whose fictionalised selves we have just spent 90 minutes. The montage is a deeply moving and satisfying resolution to a measured and exquisite film. Home Song doesn't have the seat-of-the-pants energy of Once, opting instead for a stately, formal kind of poetry, but they share a gentleness and warmth.

It is the '60s, and a Hong Kong nightclub singer, Rose (Joan Chen), sets out for a new life in Australia with her children May (Irene Chen; no relation) and Tom (Joel Lok) in tow. She's following Bill (Steven Vidler), an Australian naval officer whom she will marry and almost immediately leave. Now in her forties and still beautiful, still trying to be the party girl, she's feckless and not a good mother; her frustrated children, the victims of this flightiness, will grow up faster than they otherwise should. They're always packing up and moving from one ‘uncle' to another; she doesn't really want to relate to them as their mother, but as their friend. That's the recipe for disaster right there. What becomes apparent as the story unfolds is that she's mentally unwell, and the children are  hostage to her self-absorption.

This is young Tom's tale of his crazy mother, set against his attempts to come to grips with an alien culture. Newcomer Joel Lok is terrific as the bewildered boy-witness who can't just be a boy but must bear the burdens of responsibility which weigh so heavily upon him. Irene Chen, as his older sister, is equally excellent in portraying an adolescent girl's increasingly embattled optimism. In supporting roles, Vidler, as the kind and long-suffering Uncle Bill; Kerry Walker, as his racist, disapproving mother; and Qi Yuwu, as Rose's younger lover, are all outstanding. Joan Chen, as always, is radiant. Her porcelain-like quality has been replaced by a tremulous vulnerability, a lined weariness, which is entirely appropriate for this heart-wrenching role. "You must learn to cherish life," she says to Tom while in a mental hospital after one of her suicide attempts - but she can't cherish it herself.

Tony Ayres has said that everything that happens in The Home Song Stories happened in his life. The framing device at the beginning of the film, of the adult narrator beginning to write the story on his computer, seemed naff and clunky at first; but by the end of the film it has become moving. Ayres is a fine craftsman who pulls us in gradually until we are fully immersed in this intimate, damaged world, and the film's central tragedy is transmuted into gold.