US director Richard Linklater drew a rapturous reception at the Berlin film festival for his groundbreaking coming-of-age movie Boyhood, made over more than a decade with the same actors.
The almost three-hour-long film garnered the biggest cheers so far at the 11-day festival on Thursday.
The berlinale's Golden Bear top prize will be awarded on Saturday.
It stars Patricia Arquette and Ethan Hawke as divorced parents who had their two children, Mason (Ellar Coltrane) and Samantha (Linklater's own daughter Lorelei), before they were ready.
Arquette's character Olivia raises the children on her own in Texas with a revolving cast of unfit stepfathers while Mason Senior, in "cool dad" mode, breezes in and out of their lives in his vintage car.
Linklater switched his camera on the four actors in 2002 and only completed work on it recently.
While Arquette and Hawke gradually settle into middle age on screen, the kids quite literally grow up before the viewer's eyes, from small children to college students.
"I don't know if two actors have ever been in this position, ever, in a narrative," Linklater said.
"This whole thing was a leap of faith and a certain amount of optimism about the future - just that we would still be here 12 years from now, that things would work out."
Coltrane said the first day on set as a small boy was still vivid in his mind.
"We started production on this over 4,200 days ago but I still remember it very clearly - what the hell are we getting ourselves into?" he said.
Coltrane, who has become a visual artist, said that Linklater had not allowed any of the actors to watch the footage during the making of the film.
"I might have become self-conscious if I had been allowed to watch any of it growing up," he said.
"I mean it was a lot to deal with watching it two months ago, and very cathartic and emotional and you can imagine how difficult it would have been at 10 years old to see that and recognise myself. But it's beautiful, in short."
Lorelei Linklater, who is seen tormenting Mason with her version of a Britney Spears song in one of the first scenes, said having her adolescence play out on the big screen was far from glamourous.
"It was really, really strange, a really strange experience. It was quite painful sometimes - who wants to watch themselves go through all these awkward stages?" she said.
"It was hard, I was crying for a little while there...One year I asked him if my character could die," she said with a smile at Linklater.
The director filmed for a few days each year and said Coltrane would check with him before making any big changes to his appearance like getting a major haircut or an earring.
"He made it very clear: you can't get any facial reconstruction, anything like that," Arquette joked.
"It's very strange but life goes fast. I think that's part of what you feel (watching the film), how fast life goes."
Linklater said he studiously avoided the usual milestones of movies about growing up like a first kiss or losing one's virginity.
Instead, the film observes the subtle steps in Mason's development as he rebels against Olivia, fights with his sister, bonds with his dad during their occasional outings and develops an interest in photography.
"I just wanted to kind of capture little moments, I guess, but I had faith that they would add up," Linklater said.
The movie also depicts a tumultuous decade in American life, from the aftermath of the 9/11 attacks to the rise of Barack Obama.
Linklater and Hawke, a frequent collaborator, were last at the festival in 2013 with Before Midnight, the third part of a trilogy tracing a long-time love affair.
