AUSTIN — When Austin director Terrence Malick approached Michael Fassbender about a role in his next film, the actor accepted – with a catch.

“The one thing you’ve got to know is I don’t learn lines very fast,” Fassbender (one of the first guests on the Big Screen, BTW) said during a panel discussion Saturday morning at the Austin Convention Center.

That wouldn’t be a problem.

Malick’s most recent films are built out of an exploration of ideas and themes that happens during the shoot – heavy on improv, light on script. When they coalesce (2011’s “Tree of Life”), they’re cinematic experiences like no other. When they don’t (2015’s “Knight of Cups), it’s the most tedious experience you’ll ever have in a theater.

His new effort, “Song to Song,” opened South by Southwest on Friday night. It nominally centers on a pair of love triangles set against the backdrop of the Austin music scene. I didn’t make it to town early enough to catch it. Audience members asking questions during the discussion loved it (natch); reviews have ranged from eh to pretty bad to really bad.

Still, the exploration of Malick’s process – led by another atypical filmmaker, Richard Linklater – proved fascinating.

Fassbender said the only note Malick gave him prior to rolling the cameras was that his character – a debaucherous music manager – reminded Malick of Satan from “Paradise Lost.”

Alrighty.

Over the course of the 40-day shoot, the cast – which also includes Val Kilmer, Ryan Gosling, Rooney Mara and Natalie Portman – filmed scenes during ACL Fest and Fun, Fun, Fun Fest here in Austin to establish the musical setting. All the while, Malick says he whispered bits of procedural direction to the actors – it’s a technique used on soap operas to help move through the day’s scenes quickly.

“When things get too prepared, something takes the life out of it,” Malick said.

The result, though, is an editor’s dream (or nightmare, depending on who’s editing). Malick says the first cut was eight hours long. “We thought – is this a miniseries? It could have been” he said.

For Fassbender, the appeal was in the challenge of going out there and finding something that doesn’t yet exist, as opposed to just shooting what’s on the page.

“I liked it. I like not having lines to learn,” he said to laughs.

Still, this is a Malick film. And Malick’s gonna Malick.

“I’ll be acting my socks off over here,” Fassbender said. “And I’ll look over and Terry’s filming a beetle.”

“Song to Song” opens in theaters on Friday.