“Once” is a tiny Irish picture that made a big splash at the 2007 Sundance Festival by copping the World Cinema Audience Award and is now attracting critical raves and large audiences in very limited release. It’s an extremely simple tale about the relationship that develops between two unlikely people over several days in Dublin: one is a busker, or street musician, and the other a Czech immigrant with a young son and an absent husband. Together they record an album of the guitarist’s songs and then….well, that would spoil the surprise.

Writer-director John Carney, visiting Dallas with the picture’s two stars Glen Hansard (lead singer-songwriter of The Frames) and Marketa Irglova (who’d made an album with Hansard called “The Swell Season”), explained that while the movie remained true to his conception of a musical in which the songs were a part of the story rather than interruptions of it, in other ways it turned out rather differently from the way he’d envisaged.

“I had originally intended to put Cillian [Murphy] in it,” Carney said. “He’s a friend of mine—we’d worked together on a film called ‘On the Edge.’ I’d kind of developed the project with him in mind. Once that jigsaw piece came out of the puzzle, for me it was kind of like, there’s nobody else I want to do this with, in terms of Irish actors. Maybe I should just ask Glen, because he’s come this far and he knows Mar, and it would be really good for him to do a film like this, a musical film. And I like when you see people moonlighting, doing something different, just really surprising you. So I asked him.”

Carney had already tapped Hansard to write the songs for the movie—he’d played bass in The Frames for a few years in the early nineties (“Some songs were written, and some scenes were written, and we kind of exchanged ideas,” he explained)—and it was Hansard who’d suggested Irglova to him for the female lead. “We talked about it,” Hansard said. “In the beginning, when the project was started off, it was going to have a much bigger budget, it was going to have Cillian Murphy playing the part of Busker, and then it all started changing when John cast Mar, because John originally wanted a thirty-five-year old Eastern European woman who was going to come into this guy’s life and wake him up, give him a bit of a slap. John had written the part for an older woman, and then he met Mar.”

Irglova, who was only seventeen at the time, added, “I’ve been playing piano since I was seven, but as far as acting goes, it never even came into my head. I think I got the part mostly because I’m a piano player and a musician.”

Carney admitted as much. “Musicians over actors, yeah,” he said. “It was more important that they could sing, than that they could act.” Hansard noted that the story recalled his own experience of starting out in the business. “I was a busker—for years I was a street musician. That’s what I did,” he said. “And my mother, without telling me, went to the bank and said ‘I want to get the house done up, I want to get new furniture, I want to get new wallpaper, new curtains.’ My mother always had a good relationship with the bank. And she came to me the next day and handed me three grand—‘There you go, son, go make your tape.’ I made a tape out of that money and got signed to a major record label, and my career suddenly jumped up to a whole other level. It was totally due to my mother’s enthusiasm.”

With the casting set, Carney turned back to the script, but he said, “We really didn’t make that many radical changes. The three of us kind of improvised. I did more improvising than anyone. We definitely made things up on the spot and decided this page of dialogue or this scene could be better written by the two actors just talking.” To which Hansard added, “Which we did quite a bit.”

One of the elements of the script that didn’t change was the ending, which will probably come as a surprise to viewers brought up on typical Hollywood fare. Hansard said, “A lot of films let themselves down really badly by wrapping everything up in the last five minutes and giving you a story that trails off lovely. And what happens with those films is that you enjoy them but you forget them, because the story didn’t rip you. But some films pull you in, and then they leave you on edge. They end, and you’re left thinking about it. And that’s really the power of cinema, the duty of cinema—to make you feel something.”

And then in the spirit of “Once,” in which the songs flow naturally from the narrative, Hansard and Irglova agreed to do an impromptu mini-concert for the interviewers, with Hansard accompanying on his worn old guitar as the two sang “Falling Slowly.”

Which reminds me: check out the CD. You won’t be sorry.