HOLLYWOOD — There's method acting, and then there's what Brooklyn-born rapper Jamal Woolard endured to become Biggie Smalls for "Notorious," the recently released biopic detailing the life (and untimely death) of Christopher Wallace, also known to the hip-hop world as the Notorious B.I.G.

Woolard's tales of "Biggie Bootcamp," his immersion into Biggie's predilections and physical tics, guided by the late rapper's friends and family, have earned admiration from both fans and movie enthusiasts.

But none of his stories about gaining weight, guzzling Pepsi or donning Coogi sweaters turns out to be as relevant as the one about the cotton balls.

Inspired by Marlon Brando in "The Godfather," Woolard expanded his jowls with gauze. The act proved crucial because it changed his rhyming flow.

"Biggie had a breathing pattern that was enormous," said Woolard by phone. "Also, he had asthma. So we had to study that. I did things like hold my tongue — it's an exercise that gives you more clarity. And his tongue lay down on the bottom of his mouth. When you put cotton balls in your mouth it causes that."

Woolard faced a challenge particular to actors portraying musicians — a club that's rapidly growing with the recent uptick in musical biopics. Such roles demand more than sensitive mimicry. Whether lip-syncing or actually performing, as most do, actors must tap into their own musicality and align it with the style of the stars they play.

In the age of YouTube, the task is trickier than ever. Artists like Biggie aren't half-forgotten heroes — they live on in videos, performance clips and other archival footage available for viewing at any time on any computer.

Not so long ago, actors could riff on a myth. The carnal innocence of Val Kilmer's depiction of Jim Morrison in "The Doors" or the strength through which Angela Bassett — who plays Biggie's mother Voletta Wallace in "Notorious" — channeled Tina Turner in "What's Love Got to Do With It" emerged through attention to detail, but the stakes are higher now. An artist's fans and fellow travelers easily can call out inauthenticity. For that reason, and also because they themselves are drawn in by pop's rich archive, actors and directors are creating music in films that eerily echo the original recordings.

In "Cadillac Records," Darnell Martin's film about Chicago's Chess Records, Jeffrey Wright gives a dazzling performance as the late bluesman Muddy Waters. He brings the same nuance to scenes of Waters playing guitar and singing as to the ones in which he's interacting with his wife or close friends. Wright said he pored over photographs and film clips of Waters to develop his stance.

"He had a very specific way of moving," said Wright by phone from New York. "He held his body with a sort of coiled rigidity. In some ways, he vibrated from within. And there's a sideways movement. It's almost as though he's emerging out of these constraints."

For Wright, performing as Waters was a way of tapping into a musical birthright and paying tribute.

"That we sing in this movie (instead of lip-syncing) is an homage to the potency of these people, and it's also an homage and a lifting up of our culture," he said. "We're going back and discovering the language of the blues, which is an essential American language with which we attempt, through this movie, to share some breath — to literally share our breath with this cultural legacy."

Such dedication doesn't shock coming from Wright, one of today's most lauded actors, yet immersion is becoming the standard for music-based films. Joaquin Phoenix and Jamie Foxx hit career high points for their turns as, respectively, Johnny Cash and Ray Charles in recent biopics; since then, Foxx has maintained a side career as a singer, while Phoenix has talked of abandoning acting altogether for music.

In last year's "Control," Sam Riley went so far into his performances as the late Joy Division singer Ian Curtis that it's difficult, even for fans, to tell them from the real thing.