Actor Johnny Depp has concluded his testimony in the defamation case he filed against ex-wife Amber Heard, saying he was the victim of domestic violence in their relationship and was "broken" by the time their marriage fell apart.

Mr Depp's fourth day on the witness stand in a Virginia court ended with his attorneys playing audio from a conversation that took place after Ms Heard had secured a restraining order against him in 2016.

The "Pirates of the Caribbean" star said he agreed to Ms Heard's request to meet in a San Francisco hotel room because he thought she might retract her accusation that he had abused her.

In the recording, Mr Depp proposed that the couple issue a joint letter saying they loved each other and the media had created a storm around them. The suggestion was an attempt to find a "peaceful settlement," Mr Depp said.

Ms Heard, known for her role in "Aquaman," resisted the idea and challenged him to go public with his claim that he was the one who had suffered abuse.

"Tell the world, Johnny," she said. "Tell them I, Johnny Depp - a man - I'm a victim too of domestic violence."

Mr Depp said he responded: "Yes, I am."

The 58-year-old actor is suing Heard, 36, for $50 million. Ms Heard has counter-sued for $100m, saying Mr Depp smeared her by calling her a liar.

In another audio clip from the San Francisco meeting, Mr Depp threatened to cut himself with a knife.

"That's psychologically, emotionally where I was," he said. "At the end, I was broken ... I thought the only answer is here, take my blood, that's all I've got left."

The case hinges on a December 2018 opinion piece in the Washington Post.

The article never mentioned Mr Depp by name, but his lawyer told jurors it was clear Ms Heard was referencing him. The couple's divorce was finalised in 2017.

Amber Heard pictured in court last week

Earlier, Ms Heard's attorneys introduced news articles that they said showed Mr Depp's behaviour had already harmed his lucrative movie career well before Ms Heard's piece.

Headlines included "Why are all of Johnny Depp's movies bombing at the box office?" and "Where did it all go wrong forJohnny Depp?" The articles, published before Ms Heard's piece, claimed Mr Depp drank vodka for breakfast and was late to movie sets.

Mr Depp said that as a longtime Hollywood star he was subject of "hit pieces".

The actor testified that Ms Heard would slap or shove him when the couple disagreed and once threw a vodka bottle at his hand, cutting off the top of his right middle finger.

In a separate legal case in Britain, Ms Heard denied throwing a bottle and severing Mr Depp's finger. She said she threw things only to escape when he was beating her, and once punched him because she feared he would push her sister down the stairs.

Mr Depp, once among the biggest stars in Hollywood, said he never struck Ms Heard or any woman and that Ms Heard's allegations cost him "everything".

A new "Pirates" movie was put on hold, and Mr Depp was dropped from the "Fantastic Beasts" film franchise, a "Harry Potter" spinoff.

Ms Heard's attorneys have argued that she told the truth and that her opinion was protected free speech under the US Constitution's First Amendment. In opening arguments, Ms Heard's attorneys said Mr Depp physically and sexually assaulted her while abusing drugs and alcohol.

A state court judge in Fairfax County, Virginia, is overseeing the trial, which is expected to last until late May.

Less than two years ago, Mr Depp lost a libel case against The Sun newspaper that labeled him a "wife beater". A London High Court judge ruled he had repeatedly assaulted Ms Heard.

Mr Depp's lawyers have said they filed the US case in Fairfax County, outside the nation's capital, because the Washington Post is printed there. The newspaper is not a defendant.