Mark Duplass has done it all on a film set -- writing, directing, editing, producing, acting -- and in "Safety Not Guaranteed" he adds another credit to his already-lengthy IMDb page: playing the zither.

Duplass -- who was the lead singer of the band Volcano, I'm Still Excited!! -- stars in the upcoming offbeat indie romance as Kenneth, a Washington state resident who places a classified ad in his local paper looking for a time travel partner. (If that sounds familiar, it's likely because you remember the 2005 classified ad-cum-internet meme on which the film is loosely based: "Wanted: Someone to go back in time with me. This is not a joke. You'll get paid after we get back. Must bring your own weapons. Safety not guaranteed. I have only done this once before.")

Rather than go for the easy joke, "Safety Not Guaranteed" features ample pathos, as Kenneth forms a relationship with Darius (Aubrey Plaza), a young magazine intern sent to cover his story.

"My job was to bring the heart and try to find a genuine connection with Darius and build something that was hopefully sweet," Duplass told HuffPost at the SXSW Film Festival in March. "Bring that non-cynicism that is the essence of Kenneth into the movie. Try to -- for lack of a better word -- infect Darius with it and bring her my way."

Part of that "infection" comes when Kenneth pulls out his zither -- a string instrument used most famously in the score of "The Third Man" -- and plays Darius a love song. Called "Big Machine," the tune is like "Safety Not Guaranteed" itself: heartfelt, sweet and even a little funny.

"We talked a lot about how we wanted to approach music in the film," composer Ryan Miller told HuffPost Entertainment. "That was written into the original script: he picks up a zither and plays a song."

Miller is new to the film-composer game, having been the lead singer of the band Guster for the last 20-plus years.

"It played to my strengths: melody and arrangements," Miller said about writing music for films. "I really like movies, and I really like the relationship of working with directors. Ever since then, I've been trying to figure out how to make it work."

In this case, "making it work" included Miller teaching himself how to play the zither during the writing process of "Big Machine."

"I sent it to Mark as a QuickTime file with my wife filming me. Like, 'This is how you play it,'" he said. "He really can play. The performance in the film is him. That's him playing and singing. I think they did two takes. It was kinda cool because Aubrey hadn't heard the song either. So that's her reaction -- it's genuine. Like, 'Wow, I didn't know you could play it. That's kind of a cool."

Check out Duplass' version of "Big Machine" exclusively below. The song will be available for download as part of the film's soundtrack soon.

"Safety Not Guaranteed" hits theaters in limited release on June 8. Stop back to HuffPost Entertainment closer to the film's release for more on Miller's transition from rock star to film composer.

LISTEN: "Big Machine" from "Safety Not Guaranteed"

WATCH: "Safety Not Guaranteed" Trailer

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