In the Irish musical community, Bono should be a little envious of Glen Hansard: While the U2 frontman spends his days dodging hoards of paparazzi around the world on his Nobel-elect missions, Mr. Hansard only has to dodge fans on the streets of his home town. But that’s not to trivialize the scope of his ambitions: He is the lead singer of beloved Irish rock band the Frames, which has an enormous following in its home country and a smaller but cultish fan base in America. While Bono can’t take a step without being breathed upon by admirers, Mr. Hansard can walk around in public and do things like a normal human being. Like filming a movie, for instance.

Okay — normal humans don’t act in movies. But Mr. Hansard’s easy going persona and calm demeanor make it seem that one has. Director John Carney recruited the head Frame for his latest rock drama “Once,” a love story based on original songs composed by Mr. Hansard and the Czech singer songwriter Markéta Iglová, knowing well that Mr. Hansard would be a perfect fit for the film: The director was once a bassist for the Frames, and directed some of the band’s early videos. Mr. Hansard is n’t a stranger to the silver screen; he played the lead guitarist in Alan Parker’s 1991 film “The Commitments,” about a working-class Irish band struggling to bring American R&B to the streets of Dublin.

The sentiments behind “The Commitments” and “Once” aren’t very different, and Mr. Hansard’s role is essentially the same: He is a struggling street musician with dreams of making it in Dublin — or anywhere else — while trying to earn an honest paycheck and heal a broken heart.

Much of the acting in the film is improvised around performance scenes — the best way to describe the film might be “rock drama,” but the film doesn’t swing to extremes. The understated drama comes through the musical interactions and collaborations between Mr Hansard and Ms. Iglová. The singing begins immediately and loudly, as Mr. Hansard, as an unnamed vacuum-cleaner repairman listed as “Guy” in the credits, performs at night, roaring out the song “Say It to Me Now,” a lament about a lost love. Ms. Iglóva plays a Czech immigrant (“Girl”) who stops to listen to the street musician and asks uncomfortable personal questions about the woman who inspired his songs. Within 10 minutes, the scene changes to daytime, Girl gets a Hoover repair hook-up, and Mr. Hansard and Ms. Iglová are in a music shop, performing a duet on piano and guitar.

The storyline could not be simpler: Guy is getting over a lost girlfriend who ditched him for the big city, and Girl is raising her small daughter with her mother while she pines for her Czech husband, who refused to move to Ireland. Almost immediately after meeting Girl, Guy decides he wants to move to London to be closer to his girlfriend. In order to do this, he needs an album: He recruits Girl and three street musicians to be his band. He spends time alone in his bedroom playing guitar and records an amazing collection of rock-folk songs after securing a loan from a rock-obsessed banker. Girl works as a housekeeper and a flower merchant, all the while composing songs in her head.

The love story seems like a recipe for success for Guy and Girl, but the ending is not predictable, nor is it even central to the film’s ultimate success. In at least two scenes, Girl almost scoffs at Guy’s idea of getting together. The “love” between Guy and Girl emerges through a mutual sense of loss and a love of playing songs to get over that loss. It’s a love that music fans (especially fans of Mr. Hansard’s music) can comfortably tap into, a kind of indulgent, ephemeral mentality that allows those who are hurt to lose themselves temporarily in song. Girl and Guy share an immediate common bond in this way, one that is translated by the actors through short conversations and pensive glances indicating that while Girl and Guy are on the edge of romance, they are too trapped in their own fantasies to risk loving anyone else.

Since the dialogue takes an obvious backseat in “Once,” the film is essentially a tribute to the power of Mr. Hansard’s rock. Some might feel the music is too sappy or overwrought, but that’s just Mr. Hansard’s way of singing: He has an urgent, painful yelp to his voice that cuts to the heart of his character’s anguish. For fans of the Frames, or just of sincere, well-made folk music, the film is a great excuse to sit back and watch him perform new songs. For everyone else, “Once” is a testament to the power of listening to a song and believing, even for a moment, in the love of friendship and music.