Rock icons U2 descended onto the Toronto International Film Festival's red carpet on Thursday for the premiere of new documentary From the Sky Down, admitting to nervousness over letting fans into their private world of making music.

The movie, which is the first documentary to open the Toronto film festival in its 36-year history, looks at the creative process of making their 1991 album Achtung Baby, tensions back then in the band.

Singer Bono and guitarist The Edge took to the festival's opening night stage and confessed that even superstars get nervous when entering a new arena -- from music to film.

We are very protective of our privacy, particularly the creative process, not just because we are precious, which we are, Bono told a laughing audience, before confiding that the fear was in letting audiences see them struggle to make music.

If you knew what went into the sausage, you wouldn't eat it, Bono said.

The Edge added that it was shocking to see a lot of the old film footage from 20 years ago and to realize how close our band came to disintegrating at that particular moment.

The appearance of Bono and The Edge made the opening night screening one of the hottest tickets in town at the 11-day festival where other rock documentaries about Pearl Jam and Neil Young are getting top billing.

The festival, a widely-watched event often seen as a starting point in the movie industry's annual Oscar race, features a long list of Hollywood royalty, from Brad Pitt and George Clooney to Keira Knightley and Glenn Close.

U2 MAKES TIFF HISTORY

But the opening belonged to a nonfiction film for the first time in festival's history, and organizers noted both the event and U2 originated in 1976.

The band soared to rock stardom in the 1980s, and Achtung Baby was seen as a daring reinvention following the huge success of 1987's Joshua Tree and 1988's somewhat less-well received Rattle and Hum.

This film isn't just about the biggest band in the world, director Davis Guggenheim told the audience. It's really just about four musicians trying to make music.

From the Sky Down opens as U2 is about to play the Glastonbury Festival for the first time this year and is looking to rework older songs. As Bono says: there comes a time when it is dysfunctional not to look into the past.

It then looks back at the rise of U2 through early film footage and leads up to the making of Achtung Baby, which was influenced by industrial and electronic music and featured the hits One and Mysterious Ways.

I had goose pimples witnessing how they did it, said Guggenheim, whose 2006 global warming film 'An Inconvenient Truth' won the Academy Award for best feature documentary.

I don't think really it's a film about our band in as much as it's a film about the creative process. If you're interested in that, you're going to be interested in this film I think, but I find it excruciating, Bono said on the red carpet.

From the Sky Down is just one of a number of high-profile documentaries at the festival. Others offer audiences a look into personalities like Sarah Palin, as well as a murderer on death row and comic book fanatics. There's also a 15-hour epic that chronicles the history of film.

But documentaries will likely be overshadowed by stars such as George Clooney, who will turn out for The Ides of March, that he directed and stars in, as well as The Descendants, in which he portrays an indifferent husband and father forced to reexamine his life.

Pitt stars in Moneyball, based on the true story of Billy Beane, a professional baseball manager who reinvents his team, while David Cronenberg's A Dangerous Method, starring Viggo Mortensen and Keira Knightley, will be tested for audience reaction after runs at other festivals.

Eyes will also be watching Glenn Close in Albert Nobbs, a drama the five-time Academy Award nominee co-wrote in which she plays a woman pretending to be a male butler set in 19th century Ireland.