Mumbai, India (CNN) -- Bollywood has a unique formula for success that the world outside of India is largely unaware of.
There's a whole industry of people who prop up Indian cinema and help make Bollywood's famous song and dance routines a hit.
These so-called "playback singers" masterfully sing the songs. But you won't see them because on screen, they are replaced by actors who lip-synch the tunes.
It's a well-established technique, which employs about 200 people.
"Because it's such an integral part of the films and because the songs are such an integral part of story telling they've evolved specialists," composer and playback singer Vishal Dadlani said.
He and co-collaborator Shekhar Ravjiani have become two of the hottest playback singer/composers in Bollywood. Such is their popularity that they're known simply as "Vishal & Shekhar."
Gallery: Bollywood's formula for success
"Whether we're in the studio, whether we go for a drive, whether we're sitting in a coffee shop somewhere, music is on all the time. We're just composing, we're just writing stuff so, it's beautiful. It's the best job in the world," Ravjiani said.
They produced one of this year's blockbuster hits, "Sheila ki Jawani." It's one among many of their songs that can be heard played over and over again on Indian radio stations.
A few of Bollywood's playback singers have become as famous in India as the actors who lip-synch their music and some have even been recognized outside of the country for their talents.
Two-time Grammy Award nominee Asha Bhosle is one of them. Her voice has enraptured audiences for 65 years. Now at the age of 77, she's still belting out hits.
She's full of life and her voice is still powerful. When she walks into the studio one night at 7, she says she's been up since 5 a.m. and she will work until almost midnight.
"First I sing in the house Indian classical music, (to train) my voice. After that I come to the studio, they give (me) a song, and they tell me that this is what you have to sing and I learn right then," Bhosle said.
It's an interesting mix of old techniques and new technology. Bhosle is handed the words of the song that are literally handwritten on a piece of paper. The melody is then played for her on a guitar until she has it and then she steps to the microphone.
So whether a film actually does well at the box office or not -- if the music starts by doing well, you've got a potential hit in terms of revenues from the other sources as well.
--Atul Churamani, vice president of Saregama record label
That's when technology takes over. The guitarist has already come to the studio and recorded his bit so Bhosle puts on headphones, listens to the music and sings her part.
"In two, three hours, (we) record it." Bhosle said.
Each part is recorded separately and then brought together electronically in the studio.
Bhosle says technology takes some of the soul out of the process but admits it is much easier than when she first started. She used to have to stay up all night because everything was done live and the song had to be perfect all the way through. One tiny mistake by any of the musicians and everyone had to start over again.
Her work ethic and talent explain how it's possible that she's sung more than 13,000 songs. (She's been featured in the Guinness Book of World Records for the most number of songs recorded.)
She is adored by her fans but is very aware that this isn't just an art but a business as well.
Bollywood brings in an estimated at $2.3 billion. Some analysts say the industry wouldn't be anywhere near as profitable without the songs playback singers like Bhosle belt out.
Bollywood soundtracks are released on the radio weeks before the movie opens. The idea is to get people hooked on the music, which then reels them in to the theaters.
"So literally, music gets bums on seats and it does help the producer even sell other rights like satellite rights, DVD rights, etc.," Atul Churamani, vice president of Saregama record label, said.
It is going to be in the past one day and you will see most of the actors will be singing themselves.
"So whether a film actually does well at the box office or not -- if the music starts by doing well, you've got a potential hit in terms of revenues from the other sources as well."
Still, much of the glory and money goes to the beauties and hunks on screen. That begs the question: do these behind-the-scenes singers ever get jealous of their lip-synching counterparts.
"No, never," Bhosle said, recalling that a "very long time ago some producer asked me can you work in the film? I said no. He said, why? So I said I see my face every morning, so I will not!"
Bhosle thought she just wasn't pretty enough and has stuck to singing behind the scenes.
But times are changing, according to renowned director, screenwriter and producer Subhash Ghai, who also runs a film school on the outskirts of Mumbai.
"People are recognizing more talent than faces you know. Previously it was that they wanted a handsome face and a great voice. Now they want actors," Ghai said.
"It is going to be in the past one day and you will see most of the actors will be singing themselves."
The younger generation of playback singers is already beginning to pop up on the big screen every now and again, and they're on television programs too.
Now not only are Vishal and Shekhar's names on movie posters, but their faces are in videos and on television. And even 77-year-old Bhosle is making a career change.
This year for the very first time, she told CNN, she will be the leading lady in front of the cameras. She'll be her own playback singer in a movie called "Maaee," which means mother.
"(I'm) excited but also very scared. It's something new for me," Bhosle said. She added: "You know in life, you have to every time do something new."
