Director Amy Berg managed to land all the “big gets” she needed for her documentary, “Janis: Little Girl Blue.”

She got interviews with Kris Kristofferson, and the surviving bandmates from Janis Joplin’s three-band career. There are surviving boyfriends, including “Country” Joe McDonald, and a surviving girlfriend.

And she rounded up the two biographers — sister Laura Joplin, and Joplin’s road manager John Byrne Cooke — whose books bookend the life of the great ’60s soul singer. That granted Berg access to the many letters Janis wrote to family and friends (read from in the film by singer Cat Power), and to the behind-the-scenes world of her stardom and the drug abuse that would lead to her untimely death.

“Little Girl Blue” is thus definitive, a thorough portrait of this “American Master”  (it will appear on PBS in 2016, after a limited theatrical release this November and December.

The arc of her musical life has never been more understandable, from folk to folk blues to hard blues. Her growing understanding of how to use her voice is explained (ripped from the pages of Cooke’s book) and explored through footage from shows in San Francisco to Woodstock, Europe to Canada.

The performances are almost uniformly hair-raising — her command of the blues patter and scat between verses of the epic songs of her repertoire.  “Cry Baby,” “Tell Mama All ABout It,” “Me & Bobby McKee,”every song serving up a another “Piece of My Heart.”

Her TV interviews range from the bitter/bittersweet one from the night she went to her Port Arthur, Texas high school reunion, to her free-wheeling chats with Dick Cavett. The self-adoring talk show host has never come off warmer than he does in talking with Berg about Joplin. She was at her most unguarded in TV conversations with Cavett, who asked tough questions with a hint of concern and tenderness that will surprise you.

We learn who her biggest influence might have been — Otis Redding. We see just what it took to get her on stage and on film in the 1967 Monterey Pop Festival from filmmaker D.A. Pennebaker.

Her bandmates — Dave Getz especially — talk about the good and bad influences swirling around her, and how she “turned into a caricature” of the earthy Blues Mama persona the media gave to her.

“Little Girl Blue” is a terrific film, not as moving or damning as this year’s Amy Winehouse expose, but a warm piece of cinematic scholarship. Berg rounds up all we remember and has those who knew her best explain those memories for a musically revealing portrait of a mercurial talent who has been dead far longer than she was alive, but who seems as vital and relevant today as she must have on the cusp of the ’70s.

MPAA Rating: unrated, with substance abuse, nudity, profanity

Cast: Janis Joplin, John Byrne Cooke, Laura Joplin, Dick Cavett, the voice of Cat Power
Credits: Directed by Amy Berg. A FilmRise/PBS release.

Running time: 1:43