Comedy animation feature "Sing" premiered at the Toronto Film Festival on Sunday to an enthusiastic reception from filmgoers before Academy award winner Jennifer Hudson and singer-songwriter Tori Kelly performed songs from the movie.

The film tells the story of Buster, a Koala bear show-biz impresario voiced by Matthew McConaughey, who tries to save his struggling theater by hosting an "American Idol"-style singing competition.     His idea quickly spreads throughout the animal kingdom, attracting a wide range of contestants, from a mother of 25 piglets, played by Reese Witherspoon, to a porcine punk rocker, played by Scarlett Johansson.

McConaughey said the best part about working on the film, which is scheduled for release in December, was getting to feel like a child again.     "I don't need to get serious about anything," he told reporters on the red carpet. "There's not a big statement to make here. It's very human, the story, but it's fun."     Johansson called the chance to use solely her voice in a role "kind of liberating."

"You're really just able to kind of give it everything you have and be able to be loud and proud and then pull it back and play with the vocal nuances," she said. The movie has a soundtrack to appeal to all ages, featuring more than 85 hits from the 1940s to the present day, prompting an audience of 2,000 at Toronto's Princess of Wales Theatre to clap along and applaud throughout.

Witherspoon said she expected "Sing" to be just as enjoyable to adults as to children.    "I play a mom who has 25 kids, and I think a lot of parents can relate to the idea that you give up a lot of your own dreams for your children," she said. "I get to, through the singing competition, have my chance to be a singer, and it's a really sweet, wish-fulfillment moment."

Hudson and Kelly gave a joint performance following the premiere. Kelly first performed the Stevie Wonder classic "Don't You Worry 'Bout A Thing," receiving a standing ovation before being joined by Hudson to perform Leonard Cohen's "Hallelujah."

Hudson then closed the show with a performance of The Beatles' "Golden Slumbers."

The film was written and directed by Garth Jennings, best known for Disney's big screen adaptation of Douglas Adams' "Hitchhikers Guide to the Galaxy" in 2005 and "Son of Rambow" two years later.