Richard Linklater's coming-of-age film Boyhood is both intimate and epic

The buzz started the moment Boyhood premiered at the 2014 Sundance Film Festival. For 12 years, Richard Linklater had been working on a secret project, shooting one week a year with the same cast. Finally it was ready. The story, which charts the growth of Mason (Ellar Coltrane), a boy from Texas, over a dozen years, was a coming-of-age story like no other.

While Linklater has dealt with the passage of time before - most persuasively in his Before ( Sunrise, Sunset and Midnight) trilogy - Boyhood was an unprecedented experiment. "I think you've got to be a little crazy to contemplate such a thing," the filmmaker laughs, saying the idea of shooting over such an extended period of time came as a solution to a problem.

"I wanted to make a film about childhood, but I couldn't pick a spot. I couldn't pick my moment that seemed worthy of the whole thing. So it was having the big idea of, 'Well, how about a little bit of it?' and let it just unfold over time," he says.

Although Mason is a central figure, Boyhood is not just about his life. Along for the ride are his sister Samantha (Lorelei Linklater, the director's daughter) and his mother Olivia (Patricia Arquette), who begins the film by separating from their father, Mason Snr (Ethan Hawke). The cumulative effect of what follows is extraordinary; a microscopic look at the little moments in life that's intimate in its emotions, epic in its ambitions.

"Everything about it was technically impossible or really, really impractical," says Linklater, a boyish 54-year-old. To begin with, the funding required an annual cash injection from a financier willing to wait 12 years before seeing a return on the investment. When he first met with producers, they simply couldn't "wrap their head around it", he says. "They said, 'We're not a bank. We can't just give money out'."