Mat Whitecross also says documentary will show fans what the Gallagher brothers are really like.
The director of new Oasis documentary Supersonic has said that the film could easily have been over seven hours long.
It is due for release on October 2 and documents the Manchester band's rise to fame from 1993-96.
"It [Supersonic] could have easily been over seven hours long," Whitecross explained. "We did 12 interviews with Noel and the same with Liam. We did about 20 hours with both of them. We'd talk to Noel and Liam and it was like we'd created a conversation between them even though they weren't in the same room.
"Noel was like 'I don't want it to be a bunch of grey haired middle aged rockers talking about how good things were in the old days'. But we kept it in the present by doing these audio interviews."
He also said despite the ongoing feud between the Gallagher brothers, they were both very honest about each other during the interviews.
“We did separate screenings for Noel and Liam," he explained. "But in the interviews with Liam I said 'Well obviously you started the band' and Liam would say 'Yeah but Noel would never admit to that' and I would go 'No that's what Noel told me last week' and he'd be like 'Really? Alright, OK'.
"I realised they were both trying to be as honest as possible about it. Noel was very open. It's pretty amazing some of the things he says about Liam. He said Liam was better looking than me and funnier than me and he wore better clothes than me but he wants my talent."
Whitecross also argued that film will present a true depiction of the Gallagher brothers.
He added: "For whatever reason because of all the tabloid bullshit and because of the caricature of them that was made through the years people have forgotten what they're really like and that was one of the things we really wanted to set the balance right and just go look they're smart, passionate fucking funny people who deserve to be right up front alongside The Rolling Stones, The Beatles all these people.
"The caricature that persists is that Noel is the cold, calculating talented one and Liam is the chaotic one but I think there's so much more to them than that. I think there's a lot introspection in Liam. He's incredibly perceptive about his own character and his weaknesses. He's got an amazing psychedelic mind and I think if you get in there some of the stuff he says is like poetry. You have to write everything down. It's fucking brilliant."