"Written and Directed by Casey Affleck" read the end credits to his debut feature I'm Still Here, something he dismissed as a "union thing" when asked about it at yesterday's press conference. But whatever the director says, debate about how authentic this film is looks set to run and run. Ostensibly, the film follows Joaquin Phoenix as he quits acting and stages an unlikely bid to become a hip hop artist. But elements of the film seem a bit too convenient, for instance there are multiple cameras with all the angles covered, leaving it sometimes feeling like a Christopher Guest or Larry Charles faux documentary rather than the real thing. And the film adheres to elements of film-fiction structure (things mentioned always have a plot functionality and are usually a set up for something later). At times the film is also rather too exaggerated to be completely legitimate. Coming close to resembling Borat, as in one scene Phoenix's friend deficates on his face whilst he is sleeping. But there is always something that pulls you back and makes you think it's real again. In that respect it's similar to (though way better than) Banksy's Exit Through the Gift Shop. We see Phoenix order a pair of prostitutes whilst repeating "I'm gonna smell that girl's butthole" over and over. When they turn up, he literally does coke off a hooker's breasts. It feels like Affleck and Phoenix are playing up to a clichéd image of stardom. At least you hope that's what it is, or the Walk the Line actor is really very disturbed, and the director (his brother-in-law) more than a little exploitative. There is no question, it is edited together for maximum humorous (as opposed to dramatic) impact, in a way that would be odd if Affleck has any love for his friend. There are even bits that feel straight out of a candid camera show, as the former actor hugs stars, including Bruce Willis and Ben Stiller, holding them for a really long time as they awkwardly try and pull away. After forcing a friend to do a snow angel he turns to camera and says "that's a funny bit" proudly, whilst he consistently chastises another friend, telling him that he will come across worse than him in the finished film. In a similar way to Orson Welles' seminal F For Fake, the film seems to be playing games with the idea that it's a hoax. It is quite self-referential, talking constantly about the rumours, then circulating in American magazines, that Casey Affleck is directing a mockumentary and that Phoenix is less than earnest about his new career path. At one point a ranting Phoenix describes his acting career as "fraudulent", perhaps knowingly engaging with the audience and trying to get one over on us. Or maybe, more specifically, the media. The director mentioned at the press conference that he hates the culture of blogging about celebrities and that, having been on the end of personal and mean-spirited criticism himself, he has no time for gossip magazine culture. People have already suggested that the film is a look at celebrity and fame, and in some ways I suppose it is. But I think that this element could be a distraction. There are many shots of Phoenix watching himself on TV (such as in the fallout of that notorious appearance on David Letterman), or reading about himself online. Much of the emphasis is placed here. We see more than one montage of media reports, and we also watch - in full - a horrible web video by an online blogger. Perhaps it is the media that are the real "villain" of the piece, for the way they report Phoenix's fall with such relish and little compassion. The film also seems to show that the desire of the media to pigeonhole people maybe the biggest factor in stifling experimentation and creativity. But as I write this and convince myself more and more that it is definitely a set up, I am still plagued with doubt. For one thing, the director's frustrated and plausible denials at the press conference left me fairly convinced. But mainly it is Phoenix himself that leads me to wonder if it could be real. Not only is he so faultlessly consistent the whole time, but there is also the fact that the film took a year and a half to make - and that is a long time to be in character. Sacha Baron Cohen can do it, but he isn't playing himself. In fact, he is unrecognisable to most people when he isn't one of his creations. But Joaquin Phoenix is playing himself. He had nowhere to hide and laugh about it. And, if it's a joke then it is a risky one - as he alienates and insults people all over the entertainment industry. Maybe, as is so often the case, the boring answer is true and it's a little of column A and a little of column B. Perhaps Phoenix is as tired with acting as he claims and really has retired, but maybe this film is his elaborate joke. A parting shot to an industry he no longer cares for, if indeed he ever did. In the end though, it really doesn't matter either way. Whether it's down to a genuine absurdity or to a dedicated genius performer (he's kept this act up for two years now), I'm Still Here is really funny. I was in stitches for long spells of it and had the best time I've had in any film here. I especially loved the moments were Phoenix reflects on his movie career: "I should have been in Revolutionary Road. I do Reservation Road, it sucks and gets no nominations." Or when he complains about his relatively minor celebrity to Affleck as they both prepare to appear in a star-studded play to honour the late Paul Newman: "you do a scene with Hanks and with Jack . With all due respect, I'm with fucking Danny DeVito." There have been better films, and even greater experiences (Black Swan was emotional and intense beyond comparison) than I'm Still Here at this festival. But no film here has been more purely entertaining. Affleck more than deserved the long standing ovation given to him at the film's conclusion in a near-full Sala Grande. As to what the future holds for him as a director, it's hard to say. This film is certainly a one-off and it gives no real clue as to his style. As for Phoenix, the future is even less certain. But, whatever the truth, he just turned from "the bad dude from Gladiator" and established himself as fascinating, mercurial and maybe even iconic.