There has been a lot of speculation in the run up to the Venice premiere of Casey Affleck's documentary feature I'm Still Here, which has played out of competition today. Many have wondered whether it is an elaborate hoax or mockumentary ever since it was first announced. And, judging by the questions at this morning's press conference, many are still unsure what to make of it. I'm Still Here follows Joaquin Phoenix, star of such films as Gladiator and Walk the Line, as he quits acting and re-dedicates himself to hip hop music. Phoenix was not in attendance at the conference, prompting one of the first questions: "why isn't he here and whose decision was it?" Luckily Affleck himself was on hand to answer. "He's trying to embrace the film... he's not hiding from the movie" he said, telling us that Phoenix is in Venice but probably won't be attending any of the screenings: "his presence here is a gesture". "I hope he'll support it but in what capacity is up to him." Never cracking a smile, Affleck repeatedly - and with growing frustration - insisted that the film is serious. He batted back many of the questions saying he wouldn't spoil the film by discussing specific scenes. When one reporter said a moment in the picture was "obviously fake", he responded with surprise and maybe a little discomfort. "I haven't shown it to an audience before and got to speak to them after, so it's interesting that you react like that". The Observer's Jason Solomon's asked the director how he responds to cries of "hoax". He quickly replied with the word "elliptically", before stressing again: "I can tell you: there's no hoax. It never entered my mind until other people commented on the movie." Much has already been made of the film as a comment on celebrity culture, and the director admitted that it couldn't help but be ("I'm not sure what it says about celebrity, but whatever it is it's not very nice"). But for him the themes were of "friendship, ambition and the dreams of an artist". Apparently Gus Van Sant told him once, on the set of a movie, that "the themes should find themselves", and Affleck says that he prefers to work with that principle in mind. Phoenix is Casey Affleck's brother-in-law and many wanted to know how, if the film is for real, the director could watch him acting this way. "It's a very compassionate portrayal" he said in defense of the movie, revealing that he had total access to his subject for a year and a half of shooting: "I have a lot of love for him and I don't feel like that's been compromised at all." In spite of this, he described the film as an "opportunity to pull the curtain back" on what he called a "celebrity meltdown" and conceded that his friend may not be entirely pleased with the result: "It's probably very hard to watch yourself like that. It's not a character or a costume. It's his name up there." Another journalist then returned to the question of the film's authenticity, saying they were interested in the truth. "I bet you are" he snapped, before calling it "a leading question". If he wasn't being sincere then there was no way to tell. But then, he is an Academy Award nominated actor in his own right. The mystery continues.