Journalist Mstyslav Chernov has a fear that in the future, years after the war in Ukraine ends, his daughter will look him in the eye and ask, “What did you do to help end this violence?”

“I want to be able to give her an answer,” he says.

The videographer’s first documentary, “20 Days in Mariupol,” is the answer.

Chernov was part of an Associated Press crew of Ukranian journalists, along with still photographer Evgeniy Maloletka and field producer Vasilisa Stepanenko, who were the only known journalists to document the siege of Mariupol, a geographically strategic city, by Russian forces. The siege lasted 86 days, killing at least 25,000 people and likely significantly more. Most of the victims were civilians. While the war in Ukraine is not going well for Russia at the moment, it has held Mariupol since May 2022.

The events covered in “20 Days in Mariupol” begin on Feb. 24, 2022, soon afterRussian forces entered Ukraineto begin the conflict. Chernov’s camera captures rocket attacks and explosions, neighborhoods reduced to rubble, and Ukrainian soldiers evacuating civilians and trying to keep some semblance of peace. One of them tells fleeing citizens, “Don’t panic.”

Mostly, Chernov’s camera captures fear. This being the early days of the conflict, many of Mariupol’s citizens wander the streets in disbelief.Is this actually happening?

A fitness center becomes a makeshift shelter; volunteers heavily tape the floor-to-ceiling mirrors to minimize the shards of glass should the place get shelled. People use generators to charge their cell phones, but not to make calls or get news updates — cell towers are down — but to use them as flashlights.

Obviously, there is explicit detail. There are deaths in makeshift hospitals and cemeteries with numbers marking graves instead of names.

Although the war in Ukraine is still raging, “20 Days in Mariupol” is already a historical document. So much has happened in the warin the 16 monthssince these events, and graphic, front-lines reporting is now ubiquitous.

However, Chernov’s team was among the first to document what many say are war crimes by Russian troops, and it provided an early window into the conflict for Western news media.

“I wish I could have done more,” Chernov says in the film.

But he and his team did plenty, and for that, we owe them a debt.

Reach G. Allen Johnson:ajohnson@sfchronicle.com; Twitter:@BRFilmsAllen