PARK CITY - What fans may know is that The National contributed a brand new song to the Sundance featured flick "Win Win." What they may not know is that the closing credits track, "Think You Can Wait," also boasts Sharon Van Etten -- and that the rock act could also be heard in an additional film at the film festival.

The National provided instrumentals and the whole track "Cherry Tree" (from their EP of the same name) to "If a Tree Falls: A Story of the Earth Liberation Front."

I caught up with frontman Matt Berninger on my sixth night at the festival, and he explained how "Win Win" director Tom McCarthy was a "huge fan" of the band and had been listening to their music as he crafted his Paul Giamatti-starring film.

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"We knew he was a serious director," Berninger said, mentioning that he enjoyed McCarthy's directorial debut "Station Agent" and 2007's "The Visitor."

The material of "Win Win" was "just the kind of thing our music would work well for."

"It's about very normal and good people trying to do their best and the struggle to be good," Berninger says.

So upon viewing the movie while on tour, Berninger began cobbling together melody ideas and working with his wife on lyrics. When the band returned to Brooklyn, they hit cohort Aaron Dessners' home studio with Brooklyn neighbor and frequent show opener Van Etten and producer Peter Katis. All in all, "Think You Can Wait" was only completed a month ago.

"This was the first time we had written specifically for a film," Berninger told me. "We wouldn't normally do that, but Tom McCarthy's movies are so good. Watching ['Win Win'] helped inspire the way the song was written. I mean, it isn't at all narrative to what happens in the movie -- we don't mention Paul Giamatti by name or anything. But it was fun, and it's a good song, we're very proud of it."

And despite having major concerns about attaching The National's name to too many films and commercials, the band also decided to let "If a Tree Falls" at their back catalog for the score and soundtrack. Oscar-nominated director Marshall Curry -- who Berninger has known for 15 years -- used "Cherry Tree," which may be a lesser known cut to fans, for the closing credits.

"A lot of people don't know that EP... but that song worked so well," he says.

He explains that "If a Tree Falls" isn't an environmental movie so much as it is about the environmental movement, with its passionate people leading the charge. Berninger says that its story "doesn't resonate with me personally, thought I have been accused to being a terrorist."

(And that charge is true: Berninger recalled the time back in June last year when an entire Hawaiian airport had to be evacuated because he was bringing back a toy alarm clock that resembled a bomb in his luggage. He still blushed as he explained that he was "mortally embarrassed" about the incident.)

On the whole, Berninger says that The National are careful about their legacy as they license music, though, "You can't make money selling records. Licensing... is one of the few ways to help pay the bills."

Audiences will hear the "Win Win" track when the film is released to theaters on March 18. Berninger suspects that they'll release the song itself to iTunes or some other outlet as the drop date gets closer.

The band returns to the road in mid-February, in Europe, in support of their latest "High Violet." They will appear on "The Late Show With David Letterman" on Feb. 1 performing their next single from the set, "Conversation 16." They are also set to open for Arcade Fire on April 24-25 in Chicago at the UIC Pavilion and are helping to headline the 2011 Coachella Valley Music & Arts Festival in Indio, Calif., on April 17.

Watch HitFix's video interview with Paul Giamatti here. And check out our review of the film here.