Marin Alsop was the only child of two accomplished freelance classical musicians — a violinist and cellist — who gigged all around New York during her childhood. They’re the ones who signed her up for piano lessons as a tyke, and sent her to violin camp when she was older.

She grew up watching Leonard Bernstein’s celebrated “Young People’s Concerts,” not from the provinces on Saturday morning TV, but from the hall where “He talked directly to me” in between pieces played by the New York Philharmonic.

Alsop started at Juilliard at 7, attended Yale, founded her own 14 piece string “swing” ensemble, String Fever, and later got a backer to help her launch the Concordia Orchestra.

Later in life, she was personally mentored by the charismatic and hugely-influential Bernstein.

Every step of the way, she gained media attention, write-ups in the New York Times, feature coverage on New York TV and even network TV.

And STILL nobody wanted to give her a crack at her lifelong stream, to be a conductor and music director of a symphony orchestra. She remembers every time she heard “women can’t do that” and “no.” She’s held onto every rejection letter from college conducting programs.

“The Conductor” is an engaging, musically-adept documentary that tracks Marin Alsop’s dogged march to make her “first woman to head a major symphony orchestra” dream come true, taking on that job at the Baltimore Symphony, the Vienna Radio Symphony Orchestra and until 2020, with the Orquestra Sinfônica do Estado de São Paulo.

Bernadette Wegenstein’s film doesn’t just show us the family photos, early video and later footage of Bernstein’s “hugging, attacking” and effusive instruction and encouragement of Alsop on the podium. And it doesn’t just hit the highlights of her rise to the top — skipping many of the waypoints of her orchestral journey. “The Conductor” shows her mentoring, remote teaching, working with young women and men as she helps train those who will take the baton from her.

We see Alsop rehearsing and leading orchestras through the classical music warhorses — Beethoven and Dvořák, Mahler and Mozart. And we see her drilling students in “playing” the group of sometimes 100 musicians, mastering the gestures, the timing and the posture that a conductor needs to generate the sound that is just notes on a page until a conductor and ensemble interpret it.

On the podium, with her mop of hair flipping hither and yon, her face a mask of beatific intensity, she can’t help but bring to mind Bernstein’s soulful theatricality.

Think of what you’re told about “confronting a bear,” she tells her students. The idea? Make yourself as BIG as possible.

The point of it all is that being one of the first and for most of her career the “only” woman in such a prominent position in classical music — the 2018 bio-pic “The Conductor” is about Antonia Brico, who conducted major orchestras from the 1930s onward, but who never took on the role of music director at a major American symphony — Alsop is doing her damnedest to make it easier for women who follow her.

“The Conductor” doesn’t just document her efforts in this regard, it amplifies them.

Rating: unrated

Cast: Marin Alsop, Michael Cooper, Tim Smith, and Leonard Bernstein

Credits: Directed by Bernadette Wegenstein. A Cargo release.

Running time: 1:30