Oscar-nominated actress Carey Mulligan revealed she was nervous about singing on screen in Inside Llewyn Davis, as she described the film as a "Valentine" to folk music.
The 28-year-old, who lit up the red carpet at the film's London Film Festival screening in a strapless yellow Dior dress, admitted she was tentative about tuning up for her portrayal of singer Jean Berkey in the Coen brothers' musical drama.
"It was good, I had fun. I was scared in rehearsal because they were all real singers but they were all so lovely and they made me feel comfortable," she said.
Carey's co-stars Oscar Isaac and John Goodman, and filmmakers Ethan and Joel Coen - who wrote, directed and produced the movie - joined her on the red carpet. Justin Timberlake and Garrett Hedlund also star in Inside Llewyn Davis, which features a soundtrack supervised by Carey's husband, Marcus Mumford of Mumford And Sons and country producer T-Bone Burnett.
The An Education star said: "It's a Valentine to folk music. What is so incredible is they let the songs play out - they don't cut or pause them.
"The majority of the music is live. That's an incredible thing to see in a film."
Oscar, 33, and John, 61, admitted the opportunity to work with the Coens was a big draw.
"Everything about it attracted me to it. The fact the Coen brothers are doing it made me incredibly excited about it," said the Guatemalan actor-musician, who plays the title character.
John, who has appeared in previous Coens' films The Big Lebowski, Barton Fink and O Brother, Where Art Thou?, added: "This is a great story and I would pretty much do anything they asked me to do. They are great directors."
Inside Llewyn Davis, which won the Grand Prix at the 2013 Cannes Film Festival, will open in UK cinemas on January 24, 2014.