Actor Ellar Coltrane seems to gravitate away from your run-of-the-mill film projects.

His most-acclaimed role to date – that of Mason Evans Jr. in director Richard Linklater’s “Boyhood” – was filmed over the course of 12 years, allowing the actors to age naturally. (Coltrane aged from 6 to 18 during the filming).

Now 21, Coltrane is the focus of “By the River,” a film dubbed an “experimental documentary” in its press materials. What it is, essentially, is Coltrane on a train trip in the western U.S., being filmed by director Kevin Ford.

“It’s kind of a tough thing to describe,” Coltrane says from his home in Austin, Texas. “It’s an experience.”

That experience will unfold as one of more than 250 films at Birmingham’s Sidewalk Film Festival, Aug. 26-28 at venues downtown. “By the River” screens at 6:10 p.m. Aug. 27 at the Alabama School of Fine Arts’ Recital Hall, with both Ford and Coltrane in attendance.

See the Sidewalk Film Festival schedule and buy tickets.

“By the River” came about when Ford and Coltrane, brought together by mutual friend Linklater, found their initial project, a scripted movie called “Drowned,” had become too unwieldy and complicated.

“We were frustrated because we both had time last summer and wanted to make a movie and we weren’t getting anywhere,” Ford says. “Just in a conversation, one of us said, ‘I almost wish we were making a cross-country road film. It would be so much easier.’ One of our friends said, ‘Hey, I think that’s a great idea. I’d like to help y’all do that.’”

The result is “By the River,” with Coltrane taking a train through Texas, Colorado, New Mexico, Nevada, Utah and California, and Ford and his camera picking up whatever and whoever comes his way. It’s tied together with the work of Justin Stone, an El Paso-based poet and friend of Ford.

Ellar Coltrane is the star of “By the River.”

For “By the River,” Ellar Coltrane saw parts of the country he had never visited.

Ellar Coltrane hit the road to film “By the River.”

“By the River” is the first collaboration for director Kevin Ford and star Ellar Coltrane.

“By the River” takes actor Ellar Coltrane across several states by train.

The camera for “By the River” caught Ellar Coltrane on the train day and night.

Ellar Coltrane says filming “By the River” was meditative for him.

Director Kevin Ford sets up a shot with star Ellar Coltrane for “By the River.”

“It is truly a travel film, where you have a young man leaving Austin and taking a train out west and meeting people as he goes, and as he meets new people, that is altering his journey,” Ford says. “In its truest since, it’s a traveling kind of road film, and the subject of the film changes along the way.

“I felt very strongly that if we just hit the road, with Ellar being himself, just a cool, introspective guy, and my love of the country and exploring it visually, there was no way we wouldn’t end up with something inspiring,” he adds.

For Coltrane, filming “By the River” was a nice respite from the hubbub of “Boyhood,” which was released in 2014 and eventually won an Oscar for Patricia Arquette playing his mother.

“This was really wonderful for me,” Coltrane says. “After everything that happened with ‘Boyhood’ getting so much attention and getting sucked into that whole side of the industry and Hollywood, it was really refreshing for me to go out and do something like this, off the grid and noncommercial.

“I’m not sure if a lot of people get it, but the people who do get it seem to really appreciate it,” he adds. “We went out and had a meditative, therapeutic experience.”

Ford says it would have been a much different movie – maybe not a movie at all – if Coltrane weren’t involved.

“I think if I had put almost anyone else in there, they wouldn’t have had the sensitivity that he had, so I don’t think it would have led to the magic we had,” he says. “He tends to bring the depth out of the people he encounters. He tends to really bring out a sincere quality in people, and that’s so different than just a guy asking questions or having a journey that’s all about him.”

“By the River” marked the beginning of what could be several collaborations between Ford and Coltrane, whom Linklater thought were “compatible with our attitudes and similarities,” Ford says.

Already, the two have filmed “Drowned,” which finally came together after “By the River.”

“We had developed a great work flow and a shorthand language,” says Ford, who hopes “Drowned” is ready for the festival circuit next year.

Yet to be made is the initial project Ford had in mind for Coltrane – a film based on Ford’s years of filming music videos for the likes of Jane’s Addiction, Stone Temple Pilots and Bush.

“He’d be playing a version of the young me,” Ford says.

Coltrane continues to look for other projects, too, and laments the end of “Boyhood,” which made Linklater, Arquette, Ethan Hawke and others a part of his life for more than a decade.

“I do miss it,” Coltrane says. “I miss it a lot, getting to work with all of them. We worked together for 12 years, a week or so every summer. And when the movie came out, we were together pretty much a year straight doing publicity. It’s been strange not seeing them.”