Once it finally begins to focus on the mission, however, “This Changes Everything” not only becomes engrossing but reveals itself as a crucial cri de coeur. Most fascinating is an examination of the six women who in 1979 founded the Directors Guild of America’s Women’s Steering Committee, which sought to investigate the hiring practices of studios. All but one of the women were interviewed for this film, and Donahue takes his time to carefully lay out the details and takeaways of their efforts (which led the D.G.A. to unsuccessfully sue Warner Bros. and Columbia Pictures for discrimination).

It’s not a spoiler to say that the documentary concludes with a call to action aimed squarely at (predominantly male) studio heads, pointing to the recent commitment to inclusive hiring by John Landgraf, the chief executive of the FX Networks, as an example of what real action can look like. “Progress will happen when men take a stand,” an emphatic Meryl Streep says. “It’s the chivalry of the 21st century.”

I fear the message may continue to elude those who need to hear it the most. Even though Landgraf and several prominent men are interviewed, a title card notes that the studio head s the filmmakers reached out to declined to appear in the film. For the rest of us, “This Changes Everything” will frustrate, enrage and maybe even inspire.

This Changes Everything

Not rated. Running time: 1 hour 36 minutes.