Joe Boyd is working on his magnum opus. After nearly five decades in the music business, the legendary Boston-born record producer is writing a book on what he has learned about the music industry. The lessons should be fascinating and various, given his staggering range of experience. After all, he discovered Pink Floyd, contributed to the scores of A Clockwork Orange and Deliverance, worked with artists like Nick Drake, REM and Billy Bragg, and co-directed the documentary Jimi Hendrix, to list just a few of his accomplishments.

But we’re actually not here to talk about his book. We’re here to talk about two nights Boyd spent in New Temple Missionary Baptist Churchin 1972, listening in awe as Aretha Franklin recorded an album of gospel music before an ecstatic live audience. The result, Amazing Grace, went on to become one of the biggest and most beloved albums of not just Franklin’s career, but gospel music itself. A documentary of the film shot by Sydney Pollack was meant to be released with the album.

Forty-six years later, 11 years after the death of Pollack and eight months after the death of Franklin, the documentary is finally being released.

“It is odd, watching it back now,” says Boyd. “You can see young me in there – right in the first few minutes, there’s a scene of the director, Sydney Pollack, talking to a guy with a bad moustache and a green belt and jacket. That’s me! I was the head of music for Warner Bros. film at the time, so the project was sort of under my department. But when Sydney Pollack came in, it got away from me a bit and ended up in the vaults for a few years.”

Boyd is understating this disaster slightly. In 1972, Sydney Pollack was an exciting director. His Oscar-winning film Out Of Africa wasn’t to be released for over a decade, but he had been nominated for They Shoot Horses, Don’t They? and was already becoming a golden child of Hollywood. So Warner Bros. hired him to capture another star at work – Aretha Franklin was recording her gospel album Amazing Grace. This album was to be a pivotal one for Franklin. After 11 No. 1 singles and five Grammys, she had conquered R&B, but was facing criticism that she had strayed from the church where she’d first found her voice. There was also speculation that the singer wanted to act, and believed a documentary about her could not only secure her an Oscar for Best Song, but propel her into film roles.

The documentary was set to be huge. And then Pollack ruined it.

“I had some reservations before we started,” said Boyd. “Woodstock had been made by that time, but the idea of filming live music events was not that common, especially not with a multi-camera set-up where you would have to sync everything up later. I didn’t know the intricacies but I just had a feeling that it was more complicated than what people were thinking, and I knew Sydney Pollack had never done that kind of filming before. I raised it with the boss, but he dismissed my concerns.”

Boyd’s instinct was right. Pollack and his cameramen failed to use clapper boards during their 20-plus hours of footage. Without them, there was no way to sync up the recordings and re-takes of Franklin’s crooning with the images. Even professional lip sync interpreters hired by Pollack couldn’t save it. The footage was incomprehensible, and everything Pollack had was shoved in the vaults under a haze of shame, regret and frustration.

But during the recording, no-one knew the disaster that was looming. They were simply experiencing Franklin in all her glory.

“I just came to the church for the two days to watch the show,” recalls Boyd. “It was fantastic. It was such a majestic, transcendent experience from a consummate artist at the height of her powers. But apart from getting to see her, it was also almost the end of an era. We didn’t know it at the time, we thought ‘Oh 1972, what a fantastic evening, I can’t wait for the next fantastic evening.’

“But soon after, both Aretha and the whole R&B scene changed. People were doing very different types of production, sliding into disco, and that gospel-inflected funk was out of fashion by 1974. The great thing about the film is not only the setting of the church, but also producer Alan Elliot’s decision not to have talking heads, not to have explanations, not to do all the things people do these days with music documentaries. They just let the evening unfold.”

Remarkably, Elliott remortgaged his house to buy the film rights in 1988. Twenty years after that, he met Boyd for lunch, explaining that they might have finally figured out how modern technology could sync the footage. On the official credits, Pollack does not receive a director’s credit, and instead Amazing Grace is ‘Realised and Produced by Alan Elliot’.

But the complications didn’t stop there. Franklin objected to the film’s release, suing and getting a restraining order to prevent it being screened at the Telluride Film Festival in 2015. The battle over the film, and the fact that it’s only now being released after Franklin’s death, means it’s a bittersweet experience for Boyd.

“She was a complex person,” says Boyd of Franklin’s objection. “She’s on record as liking the film, she said it was wonderful. But she also wanted to get paid! She wasn’t one for lawyers and contracts – there was a rumour going around that in all her years with Clive Davis and Arista, she never had a contract. Which is wonderful, if they did that, and just worked together – but film studios don’t do that.

“She wouldn’t engage with the process, and then in later years she was ill. So it’s not as it should be. In an ideal world, Aretha should be walking down the red carpet at the premiere, getting bouquets of roses. But we showed it to the family last year and they recognised the film for what it is – a fitting tribute to an extraordinary two nights, and an incredible artist.”

Amazing Grace is in cinemas now.