With awards from the Sundance Film Festival and the Dublin International Film Festival already under its belt, the low-budget independent Irish film 'Once' finally gets a general release. There's little to the plot - a Dublin busker (Hansard) and a Czech-born street vendor and pianist (Irglová) meet on Grafton Street and spend a few days making sweet music together - but this film has the kind of charm that transcends such a bare bones description.

Glen Hansard, best known as the charismatic frontman of long-running Irish band The Frames - and, although he prefers that it not be brought up too often, for his role as Outspan in Alan Parker's film 'The Commitments' - and Markéta Irglová have worked together previously. Their 2006 album 'The Swell Season' was a memorable and heartbreaking recording. 'Once', described as a modern-day musical by writer-director John Carney (himself a former Frame) takes songs from that album and sets them in a contemporary Dublin context. Covering the events of a week, it is set in an instantly recognisable city, from the Dunnes Stores sales signs behind Hansard as he sings on the street to the influx of Eastern Europeans crammed into old Georgian buildings on Gardiner Street.

Hansard, as the nameless Guy of the film, dreams of a record deal. His girlfriend has recently left him and emigrated to London; he's raw from that loss and vulnerable. Initially unreceptive to Irglová's (playing a role called the Girl) friendly overtures, when he discovers her musical skill - she's a talented pianist and singer - they click and spend a weekend writing and recording their songs.

'Once' focuses on the people that the Celtic Tiger didn't forget, so much as sidestep. Dublin looks authentically grimy and Hansard is a habitué of the familiar haunts of the penniless - Bogart Menswear on Aungier Street, Simon's Place in George's Street Arcade - and does his socialising at a party in a friend's house. A Big Issue seller, Irglová lives in a run-down apartment with her mother and daughter. They have the only television in the building so, every evening, three Polish lads arrive to learn English by watching 'Fair City'.

Shot on the fly and improvised on the streets of the capital, 'Once' has wonderfully natural performances from the two leads. Although musicians first and actors second, they acquit themselves well in both areas. Irglová, a largely unknown quantity alongside the well-known and either loved or loathed Hansard, is luminous. The other performance that stands out is Bill Hodnett as Hansard's father, convincing as a grumpy old curmudgeon who turns out to be enormously supportive of his son's musical career.

Although insubstantial, 'Once' is a beautiful and bittersweet film with more than enough soul - and heart - to capture a wide audience. An unexpected treasure.

Caroline Hennessy