"When videos of controversial police encounters generate headlines, there's an important figure in the story that we rarely hear about - the person filming.

By the time 17-year-old Darnella Frazier started recording, George Floyd was already gasping for air, begging, repeatedly, "please, please, please".

The camera had been rolling for 20 seconds when Mr Floyd, 46, uttered three more words that have now become a rallying cry for protesters.

"I can't breathe," Mr Floyd said.

The words were slightly muffled. He strained to speak as he lay face down in handcuffs, pinned to the floor by three police officers. One of those officers, 44-year-old Derek Chauvin, pressed a knee against Mr Floyd's neck.

Why I decided not to watch Floyd's video

Ms Frazier was taking her nine-year-old cousin to Cup Foods, a shop near her home in Minneapolis, Minnesota, when she saw Mr Floyd grappling with police. She stopped, pulled out her phone and pressed record.

For 10 minutes and nine seconds she filmed until the officers and Mr Floyd left the scene; the former on foot, the latter on a stretcher.

n charged with second-degree murder over the death of George Floyd

At that point, Ms Frazier could never have imagined the chain of events that her video would set in motion. At the click of a button, the teen spurred wave after wave of protests, not only in the US but across the world.

"She felt she had to document it," Ms Frazier's lawyer Seth Cobin told the BBC. "It's like the civil rights movement was reborn in a whole new way, because of that video."

Ms Frazier, a high school junior, was not available for interview. Her lawyer said she was traumatised by what she saw outside Cup Foods on 25 May. It was "the most awful thing she's ever seen".

Cup Foods has become a memorial for George Floyd

Since then, she has seen a therapist and "is doing pretty well", Mr Cobin said.

Coping with the response to her video has not been easy either. On Facebook, where she posted the video, the reaction was a mix of shock, outrage, praise and criticism.

In a Facebook post, shared on 27 May, Ms Frazier responded to suggestions she filmed the video for "clout" and did not do enough to prevent the death of Mr Floyd.

"If it wasn't for me, four cops would've still had their jobs, causing other problems. My video went worldwide for everyone to see and know," Ms Frazier wrote.

The backlash to Ms Frazier's video epitomises the dilemma facing bystanders who capture high-profile incidents of police violence on camera. Other similar cases have shown it to be an unenviable position to be in.

When emotions run high, videos of police brutality can have a polarising quality, dividing opinion across racial and political lines. Standing at the centre of that debate can take a heavy toll.

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