NEW YORK — They say it's not over till the fat lady sings — and that means Fat Amy isn't ready to put down her microphone.

The movie "Pitch Perfect," which was released in September and grossed $65 million domestically, is also a success on the music charts, where the film's soundtrack has peaked at No. 3 on the Billboard 200 and has sold more than 713,961 units so far, according to Nielsen SoundScan. The film stars Rebel Wilson (Fat Amy) and Anna Kendrick (Beca) as members of the all-girl a cappella group, The Barden Bellas, who are battling other a cappella groups in a national competition.

Kendrick's rendition of the folk-pop tune "Cups" is helping push the soundtrack to musical heights: The song has sold one million tracks and currently sits at No. 27 on the Hot 100 chart.

"It's totally surprising," the perky, red-haired 27-year-old said. "I always figured soundtrack sales would be a part of a movie that has so much music in it ... but I had no idea we'd be into summer of the next year and people would still be talking about the album (and) buying the album."

The gold-selling "Pitch Perfect: Original Motion Picture Soundtrack" was released the week the film hit theaters. Kendrick, an Oscar-nominated actress, was in New York last week to receive a platinum plaque for "Cups," which is also a viral hit thanks to the cup routine she performed in the film, in the song's music video — which has 17 million views — and others imitating it in their own videos and posts online.

"We were like, 'OK, it's a cute song. Let's ask our audience what they think about it.' And it was enormous. It was enormous," said Sharon Dastur, program director for New York City's top station, Z100 (100.3 FM), where the song is on rotation.

"Cups" was originally just 76 seconds long, but Kendrick re-recorded a version that is just over 2 minutes and it appears on a second soundtrack from the film dubbed "More from Pitch Perfect," which was released last week.

"It wasn't already planned," said Mike Knobloch, the president of film music and publishing at Universal Pictures, of the new album. "There were just some things we couldn't get cleared or include more for business reasons initially. Once we saw there was such a demand for it, we were able to go back and release more music from the film."

The albums feature mash-ups and covers of songs like Kelly Clarkson's "Since U Been Gone," Rihanna's "S&M" and La Roux's "Bulletproof." The success of the soundtrack comes at a time when album sales are low and for soundtracks, gold and platinum plaques are rare.

"Universal was looking for partners and there were other companies that looked at this movie and passed on the soundtrack opportunity," said Bruce Resnikoff, the president and CEO of Universal Music Enterprises, the label that released the soundtrack. "We were fortunate enough to have people who saw it and believed it."

Resnikoff said the reason for the soundtrack's winning moment is because its audience includes teenagers who are constantly listening, streaming and buying music online.

"This was an album that was completely launched through a digital medium," he said. "I do think some of the same things that have hurt the soundtrack business — the digital marketplace — were essential in creating the bigger opportunities here."

Harvey Mason Jr., the Grammy-winning producer and songwriter behind hits for Chris Brown and Beyonce, said music fans enjoy new renditions of popular songs, which is evident in the success of tunes from shows like "Glee," ''American Idol" and "The Voice."

"My daughter, she's 15 and she liked it. So I said, 'Yup, that's a good sign,'" said Mason Jr., who co-produced the soundtrack.

Kendrick, who earned a Tony nomination for her debut on Broadway at age 12 in "High Society," said she's enjoying her success on the music charts, but that she isn't jet-setting to create an album and launch a career as a pop star.

"I really don't see that happening. ...This has been so amazing and such an accident that I think now there would be a real expectation for it to do well and I'm perfectly fine with being one for one and just calling it a day," she said.

Kendrick's film credits include "Up In the Air," for which she received an Academy Award nomination, "50/50" and the "Twilight" franchise. She said she's currently filming a musical and will also appear in the 2015 sequel to "Pitch Perfect." In the meantime, she's waiting to hear her version of "Cups" on the radio.

"I've been in Berlin so I still haven't heard it on the radio, so I haven't had that moment of like being in my car, like in all of those movies about musicians the first time that you hear it in the car," she said. "But then I think, like, my band would break up and we'd all do drugs and yell at each other and sleep with each other's wives, so maybe I don't need that moment because that is a foreshadowing moment that I think would end in tragedy."