Once upon a time, a feature-length documentary that did well theatrically was the holy grail of nonfiction film. But in 2015, the nonfiction world began to change. That year, HBO’s six-part series “The Jinx,” about murder suspect and real estate heir Robert Durst, aired to great acclaim and became a pop-cultural phenomenon.

Just months after the widespread success of “The Jinx,” Netflix’s true-crime 10-part series “Making a Murderer” was released and that also became a pop-cultural phenomenon. Both series officially reinvigorated the long-form, true crime docuseries format and primed audiences for ESPN’s “O.J.: Made in America.” That multi-parter premiered as a “special event” at the 2016 Sundance Film Festival and drew instant acclaim. The seven-hour, 47- minute opus screened at the Tribeca Film Festival, and had a theatrical run that qualified it for an Academy Award, before airing on ABC and ESPN as part of ESPN’s “30 for 30” series. The film/series went on to garner top documentary prizes from the National Board of Review, the DGA, the PGA and the Intl. Documentary Assn., before eventually winning entertainment’s most sought after prize: the Academy Award.

The win was controversial. The lines between film and television documentaries were already blurred, but now, “O.J.: Made in America” had all but erased those lines.

The Academy of Motion Picture Arts and Sciences responded by barring multi-part and limited series from its documentary feature category, but by then it didn’t matter. The documentary format had entered the zeitgeist. Audiences wanted another multi-hour piece of nonfiction to binge on and broadcasters were more than willing to shell out the big bucks to make that happen. The white-hot market allowed documentary filmmakers permission to embark on deep-dive investigations or carry out wide-ranging panoramas of people and events without being beholden to a 90-minute timeframe. And to top it all off, finding funding for an innovative docuseries that had something profound to say about a social issue or true crime wasn’t a problem. Companies including HBO, Showtime and Netflix got behind the format in a big way and weren’t afraid to write fat — for documentaries at least — checks.

Oscar-winning and nominated directors including Alex Gibney (“Enemies: The President, Justice & the FBI”), Joe Berlinger (“Cold Blooded: The Clutter Family Murders”) and Amy Berg (“The Case Against Adnan Syed”) are among the many prominent documentarians who have directed or are directing docuseries. Even narrative fiction royalty — Mark and Jay Duplass and Allen Hughes — have entered the docuseries market.

In other words, AMPAS’ rule change didn’t scare anyone away from docuseries. What the org’s modification did achieve was making ATAS’ Primetime Emmy for documentary or nonfiction series one of the most competitive, sought after and prestigious categories.

“Series are starting to make documentary features feel like an endangered species,” says Vinnie Malhotra, Showtime’s senior vice president of documentaries, unscripted and sports programming.

Malhotra is behind Liz Garbus’ “The Fourth Estate,” a four-part docuseries that follows the workings of the New York Times through the first 12 months of Donald Trump’s presidency.

“The Fourth Estate” is nominated for docuseries along with PBS’ “American Masters,” BBC America’s “Blue Planet II,” HBO’s “The Defiant Ones” and Netflix’s “Wild Wild Country.”

“Wild Wild Country,” which follows the twisted tale of the a followers of cult guru Rajneesh, was one of Netflix’s biggest success stories of the year. Mark Duplass, who co-produced the series with his brother Jay, says “The Jinx” and “Making a Murderer” paved the way for “Wild Wild Country.”

“Obviously true crime and murder are these salacious topics that are going to bring massive amounts of people to a form like documentary which normally only sees niche viewers,” Duplass says. “But now that [audiences] are there, they’re starting to appreciate the form in and of itself. So, not to be crude, but [viewers] come for the murder, but now they’re staying for the form. And I think there’s opportunities now for people to make documentary series that are outside of just solely, inherently salacious material. It’s opened up a whole new realm of storytelling.”

Fellow narrative filmmaker Hughes was excited to take his first dive into the nonfiction realm when he began working on “The Defiant Ones” five years ago. Hughes knew that the project, about the intertwining careers of music moguls Jimmy Iovine and Dr. Dre, would be a series. When he brought it to HBO they agreed and “doubled-down financially” on the doc, which would become a four-parter.

“I look at the documentary medium and it’s like the wild, wild, west,” Hughes says. “It’s still such a frontier to explore. There are different ways tell stories that you can’t do in features. You can spin narratives, plant seeds, drop the subject, start a new subject, come back to that subject. I had a ball with the fact that if I got bored I could just literally change the subject and go somewhere else.”

Michael Kantor is familiar with the doc frontier. A veteran nonfiction producer and filmmaker, Kantor became executive producer of PBS’ “American Masters” in 2014. He is responsible for the popular documentary series about the lives of artists and innovators. The series’ representative program this year is “Lorraine Hansberry: Sighted Eyes/Feeling Heart” about the first black woman to write a play performed on Broadway. This marks “American Masters” 18th docuseries nomination. (The show has 10 category wins.) Kantor says the current cultural climate is, in part, responsible for the recent rise in category competition.

“People are really searching for the truth right now,” Kantor says. “They want to hear something that’s not packaged for consumption and not, you know, hyped a certain way.”

Sarah Barnett, president and general manager of BBC America, agrees.

“Perhaps documentary filmmakers’ work is giving us precious perspective, a needed complement to the news cycle,” Barnett says. “[They are] helping translate our world into something we can tolerate and understand.”

BBC America’s “Blue Planet II” is helping audiences understand the ocean. The seven-part series is the second installment of the BBC Natural History Unit’s docuseries. The first, “Blue Planet,” which debuted in 2001, was nominated for five Emmys and won two.

With murderous content set among animals, the nature series’ nomination is not surprising. The producers developed their own camera system and lenses to create a stunning, can’t-take-your-eyes-off-it program.

But Barnett is quick to point out that nature series have been around for a long time and not just because of their beauty, but because the good ones have “everything.”

“The best nature series have humor, drama, characters, high stakes,” Barnett says. “They can be more edge of your seat suspenseful than the many crime docu series.”