A documentary short that looks at the evolution of the porn industry will premiere at New York City's Tribeca Film Festival, which takes place from April 20 to May 1.

Filmmaker John Waters is among the interview subjects in Smut Capital of America, a 15-minute short about San Francisco's role in breaking the hardcore porn barrier.

“It was a woman's ass, that was the first thing you see, then a woman's tits, then a man's ass, then anything before a dick,” Waters says in the film.

The documentary is directed by Michael Stabile, a veteran of the gay porn industry, who says he stumbled across the city's contributions to the industry while working on a feature length documentary about the life of Chuck Holmes, the founder of gay porn studio Falcon.

Porn before 1970, Stabile explains, was treated like narcotics: “You could go to jail if you were caught selling it or distributing it.”

The laws were also used to aggressively choke off discussions about being gay. Literature from early gay rights groups was considered obscene and subject to the same laws used to prosecute users of porn.

A landmark Supreme Court ruling, however, struck down such laws, and the porn industry evolved from pin up girls to hardcore sex almost overnight.

“It happened in 1969,” Jeffrey Escoffier, author of Bigger Than Life, says in the film. “And it happened in San Francisco.”

Waters rose to fame in the early 70s, producing cult films that straddled the line between porn and cinema.

“I think San Francisco when I came here was gayer than it is today,” the 64-year-old, openly gay filmmaker says. “South of Market there was a bar called The Hungry Hole, that was a glory hole that you put your ass though. That's fairly radical.”

Other gay-themed films premiering at the festival include GONE, which documents New Yorker Kathy Gilleran in her search for her missing gay son. Director Cameron Crowe's documentary that follows singer-songwriters Elton John and Leon Russell throughout the creative process behind their 2010 studio album The Union will open the tenth edition of the festival.