The notorious Cameroonian prison with its own record label

Empereur is one af the prison's most successful artists - the music video for his song Sa Ngando has been viewed 24,000 times on YouTube

New Bell - a notorious prison in Douala, Cameroon - is a city within a city.

The facility has its own "taxis" (inmates who whizz through congested courtyards on foot to hand deliver messages), its own law enforcement (burly prisoners who help stretched guards police the facility) and market (a string of stalls where convicts sell and buy goodies, like fried cassava and beignet pastries).

Basically, the occupants of New Bell have adapted the jail's slack laws to work for them. The clearest example of this spirit is Jail Time Records, an on-site music studio and label making mini stars out of the most talented prisoners.

Empereur, the feared leader of gangs inside and outside of the prison, has amassed 24,000 YouTube views with a music video filmed entirely in prison.

Songs from the inmates have gained fans from as far away as South Africa, the US and Argentina, while earlier this year Jail Time Records put on a huge concert for the prisoners in New Bell's courtyard.

"It's this instrument of resistance… where we can really share friendship, love and our voices can be heard," Steve Happi, the former inmate who co-founded Jail Time Records, tells the BBC's Talking Movies programme.

"We don't think anymore about the four walls - we find the freedom."

The Jail Time Records studio is rudimentary - a small, sweaty recording booth attached to a room inhabited by a solitary computer.

But it is also the site of great catharsis and creativity, as per a recent, acclaimed documentary named after the studio.

Directed by Happi and Italian artist Dione Roach, his Jail Time Records co-founder, it was filmed in New Bell over six years.

Last month it won three prizes, including best documentary feature, at New York's Tribeca film festival.

In the film, a prisoner named Stone raps into the studio's microphone: "Heart of stone, it's war. My senses shatter like broken glass.

"I'm closed and tight like a cell door. No solid ground I slip like a fish."

Stone (R), a former soldier in the presidential guard, raps and produces music with Jail Time Records

Stone, who used to be a soldier in Cameroon's presidential guard, was sentenced to 10 years in New Bell for robbery and illegal possession of firearms. He insists he is not guilty.

The film captures him trying - often unsuccessfully - to reach his young daughter Maira on the phone.

"It's been a long time. She needs to hear my voice from time to time, so she doesn't forget about h