Marketa Irglova and Glen Hansard in Once, opening Wednesday in New York (Photo: Fox Searchlight)

Admittedly, the hack in me takes comfort in the unexplainable and sometimes defaults to kismet to explain films like Once. It attributes credit where it can -- a resourceful filmmaker, two songwriters performing at unnaturally high levels -- before shrugging off the reasons it shouldn't work. You know: bad (read: no) cinematography; dodgy sound; non-actors churning through meet-cute clichés and mediocre dialogue; scenes attenuated to the point of transparency. The film's most baffling qualities are also its most soothing and reassuring. Like its American contemporaries The Talent Given Us or In Between Days, both astonishing admixtures of intellect, imagination and a busload of accidents, Once is very literally phenomenal.

The hack in me doesn't want to know more than that -- and doesn't really want you to know more than that either. There's the story, I guess, for what it's worth: A busker (Glen Hansard) and a free-spirited Czech immigrant (Marketa Irglova) cultivate a musical and quasi-romantic relationship in present-day Dublin -- quasi-romantic to the extent that will-they-or-won't-they applies primarily to the duration of their songwriting partnership. Estranged from ghost-like exes, the nameless duo share frisky, frivolous exchanges between loose, long performance sequences. And... that's basically it. The rest is in the blood, the seams, the texture. The chemistry, too, though it slackens outside the confines of the pair's creative interludes.

And of course, the chance. Like back in the '90s, when Hansard ran into director John Carney at a Dublin music shop playing a bass he didn't own. Hansard asked Carney to join a band he was starting; he told the wiry Irishman he liked him because he looked French. That band became The Frames, and The Frames got big. But Carney eventually split to make films, finding modest success in indie features and Irish TV.

"For a long time I was just strumming the guitar and writing music when I should have been writing scripts," Carney said during a recent interview in New York, where his film opens Wednesday. "So I thought, 'I'll do something with that. So I came up with this simple little story that I could hang all of these songs on. And the idea was to make kind of a modern-day musical. I really love Guys and Dolls and Singin' in the Rain -- all those films. So the challenge was to try to do a modern version of that. How do you do that? Do you put it on tape? Do you work with actors? Who do I know? So I was at a Frames gig a few years ago -- a free gig at Marley Park in Dublin -- and it just struck me."

Carney had considered Hansard among his primary consultants for the film, assuming he ever made it. Talking to the singer-songwriter after the show, however, Carney proposed a role in front of the camera. Hansard didn't take long to agree. Then it got better -- or weirder. "I said I was looking for an Eastern European woman who can play piano," Carney recalled. "He said, 'Well, I know an Eastern European woman who can play piano.' "

(L-R) Glen Hansard, Marketa Irglova and John Carney earlier this month at a New York preview of Once (Photo: STV)

Irgolva and Hansard had been collaborating for a few years, since back when her family helped coordinate a Frames tour in the Czech Republic and Irglova periodically joined the band on keyboards and vocals. Stars crossed. The two continued working through tours and hiatuses and had a full slate of songs by the time Carney approached them. The director exhumed old numbers ("Say it to Me Now," the song Hansard plays just prior to the couple's first meeting, is from the Frames first album, released in 1996) and commissioned new ones -- fresher, more contextual.

"It was very much that dream of, 'How do you and I collaborate together on a project?' " Carney said. "Glen's a musician who's into films, and I'm a filmmaker who's into music. So we were wondering how to marry those two art forms without there being too much music -- being a concert film -- or without there being too much dialogue and not enough music. And it was such a thrill, because I have a lot of respect for these two. It was like having George and Ira Gershwin and saying, 'I didn't like An American in Paris. Will you re-record it?' "

And so they did, often in light speed and under outrageous circumstances. "He was like, 'Yeah, I like this and this and this,' " Hansard said of his director and former bandmate. " 'But I need a song called "Once." And there's a scene where she walks down the street and she comes from a shop. I need something that's got a bit of a beat.' " Hansard and Irglova wrote and recorded it overnight, and ultimately, that sequence best symbolizes the film's organic, high-functioning craft: A long, handheld take grown out of the curious confluence of heartbreak and dead Discman batteries; Irglova in her robe, slippers and headphones on the dark steps of a grocery store, stringing lyrics over her new friend's music as Dublin sleeps. Headlights pixilate the video frame. A drum machine enters. It's a muscular shabbiness -- aggressively artificial, full of syntheses.

Moreover, though, it's an entirely secret mode of sharing. In their anonymity, the characters retain the unknowable quality of all great pop music; Irglova's private creative reckoning acquires the lived-in quality of great cinema. The camerawork entitles viewers to an even more intimate proximity; you no longer simply relate to the melodies and themes, but recognize their transitory moment. "The feeling that you shouldn't quite be watching what you're watching, in a way, was part of the project," Carney told me. That doesn't mean uncanniness, though; Carney's too smart for that. Rather, it means rhythm and a knack for depicting it. The guy is a former bassist, after all.

"Glen and Marketa are non-actors" Carney added. "I realized during rehearsals that the camera up close would make them very self-conscious. So if I tried to make the film kind of beautiful or impressionistic in any way, we'd waste a lot of time on-set trying to make the thing look really good, but not actually get the performances right and the feeling of Dublin right. We had the make that decision at a very early stage: The look of the film is less important than how it feels and sounds."

And despite the accidents and luck -- the shuddering, early loneliness of those extreme wide shots in the middle of the city, or the symmetry of flared reflections in the final shot -- the hack in me knows there's an answer for most things. But Carney has it right: In its modesty and tradition, Once isn't about what you know, but rather what you sense. And having the grace to appreciate a privilege when you see one.