Kristen Stewart's Susan Sontag biopic is an "experiment" which will blend the genres of movies and documentaries.

The 'Twilight' star is set to play the renowned writer in new film 'Sontag' which will be directed by Kirsten Johnson and based on the biography 'Sontag: Her Life' by Ben Moser - and the actress has now revealed the project has a "unique format" and is going to take a long time to complete.

Speaking during a press conference at the Berlin Film Festival in Germany, she explained: "The Sontag thing will be made over such a long span of time. The format is unique. It’s a hybrid documentary, research project, experiment, film within a film type thing."

The project was announced at the film festival last year, and Stewart admitted she has no idea when it will be finished. She added: "We started last year here at the festival. I don’t know when we’re going to finish it. It’s an open-ended process."

During the press conference, Stewart also spoke about her new movie 'Love Lies Bleeding' about a gym manager who embarks on a doomed romance with an ambitious bodybuilder and she insisted she hopes it will herald in a new era of queer moviemaking.

She explained: "I think we can’t keep doing that thing where we tell everyone how to feel and sort of pat each other on the back and receive brownie points for providing space for marginalised voices, and only in the capacity that they are allowed to speak about that alone.

"We’ve all been there the whole time. I think the era of queer films being so pointedly only that is done, it’s over. Maybe they’ll keep happening, but I think it’s sort of inherent to how we’re all moving forward."

Stewart added: "I’m really kind of into the idea of unearthing sidelined perspectives and not making it all about the reasons that they’re sidelined, but their actual experience.

"What they love, what their desires are, where they come from, where they want to go. And then not feeling like you always have to stand on a ... soapbox and be everyone’s spokesperson."