Keira Knightley takes on her first major singing role in 'Begin Again'

Keira Knightley stars with Mark Ruffalo in the movie 'Begin Again.' 'The whole thing was out of my comfort zone,' Keira Knightley said. 'I am not a singer. I didn't know how to do that.'

British actress Keira Knightley, known for playing tragic heroines in period dramas, strayed into new territory with her first major singing role in "Begin Again," a feel-good film about the music industry and starting over.

"Begin Again," which opened in wide release on July 11, was written and directed by Ireland's John Carney, whose 2006 indie musical "Once" nabbed the best original song Oscar for "Falling Slowly."

"Once" was also adapted into a Broadway show and won eight Tony awards, including best musical.

Like its predecessor, "Begin Again" is laced with music and much of it is sung by Knightley, along with Maroon 5 frontman Adam Levine, who makes his film debut.

"The whole thing was out of my comfort zone. I am not a singer. I didn't know how to do that," Knightley, a best actress nominee in 2006 for her role in "Pride & Prejudice," said in an interview.

"A lot of the film was improvised, and I had never done that before. I'd say that those two were major things to be grappling with," added the 29-year-old actress, who took voice lessons to prepare for the film.

Knightley plays Gretta, a British songwriter and reluctant singer, who arrives in New York with her longtime boyfriend Dave, played by Levine, just as he is about to hit the big time.

Fame clouds his judgment and he strays, leaving a bereft Gretta on the verge of returning home when she is discovered by a chain-smoking, down-and-out record producer named Dan, played by Oscar nominee Mark Ruffalo.

"Essentially, what it is about is people falling down in life and trying to pick themselves back up, whether that is romantically or whatever," said Knightley.

Dan persuades Gretta to record her songs live on the streets of New York for a CD to revive his nonexistent career. Along the way, the two strike up an unusual friendship.

Ruffalo describes his own character's transformation.

"I like the meditation on the character's journey back to his creative self from this material world, and coupled with a mid-life crisis and a marriage that is going through a transition," Ruffalo said about the role.

"There is just a lot of fertile ground," he added about the film that premiered at the Toronto Film Festival last year.

Catherine Keener ("Capote") plays Dan's estranged wife, Oscar nominee Hailee Steinfeld ("True Grit") his rebellious daughter, and 2012 best actor Tony winner James Corden ("One Man, Two Guvnors") is Gretta's struggling musician friend Steve.

Grammy-winning rapper CeeLo Green and Yasiin Bey, formerly known as hip hop artist Mos Def, play Dan's music colleagues.

Ruffalo, whose career started in the theater, wouldn't mind if, like "Once," Carney's new film is adapted for the stage.

"I think this could be an easy move," he said. "So much of the work is already done."