The police officers, who were also Black, were charged with second-degree murder in the beating of Tyre Nichols, 29, who died in hospital on January 10, three days after being stopped on suspicion of reckless driving.
"They had beat him to a pulp," Nichols's mother RowVaughn Wells told CNN. "He had bruises all over. His head was swollen like a watermelon. His neck was bursting because of the swelling."
"I knew my son was gone, even if he did live he would have been a vegetable," Wells said, sobbing.
Memphis police chief CJ Davis said the video, which will be released after 6:00 pm Central time (0000 GMT Saturday), shows Nichols crying out for his mother.
"What I saw on this video was more of a groupthink sort of mentality. And no one took a step to intercept or intervene," Davis said on CNN. "And that's why the charges are as severe as they are."
Davis compared the video to the 1991 Rodney King beating video, which sparked days of riots in Los Angeles that left dozens dead.
"I was in law enforcement during the Rodney King incident, it's very much aligned with that same type of behavior," Davis said. "I would say it's about the same, if not worse."
- Police brutality -
Nichols's death at the hands of police also recalled the May 2020 killing of George Floyd, another Black man whose suffocation by a white police officer in Minneapolis was caught on film.
Video of Floyd's death spread rapidly, sparking a massive wave of protests nationwide, sometimes violent, and leading to scrutiny of race relations and police brutality in the United States.
President Joe Biden, anticipating outrage at the Memphis video's release later Thursday, called for calm.
"As Americans grieve, the Department of Justice conducts its investigation, and state authorities continue their work, I join Tyre's family in calling for peaceful protest," the president said in a statement.
The police officers were taken into custody after an internal investigation found them to have deployed excessive use of force and to have failed to render aid.
In addition to second-degree murder charges, the officers are also facing indictments of aggravated assault and aggravated kidnapping.
Four of the five were released from jail after posting bail, US media reported Friday, citing jail records.
"People don't know what those black police officers did to our family," RowVaughn Wells said.
"And they really don't know what they did to their own families. They put their own families in harm's way. They have brought shame to their own families. They brought shame to the black community.
"Once you see this video, and I know I didn't see it but from what I hear it is horrific. Where was the humanity? They beat my son like a pinata."