LOS ANGELES (AFP) - Ailing media mogul Sumner Redstone said he wants his former companion out of his life, repeatedly using expletives to describe her in videotaped testimony presented in court on Friday (May 7).

The 92-year-old billionaire, who is the controlling shareholder of Viacom and CBS, said he hated Ms Manuela Herzer, who brought a lawsuit challenging his mental competence after she was ejected from his home last fall.

In a halting 18-minute deposition taken at his Beverly Hills mansion on Thursday, Mr Redstone repeatedly referred to his former live-in girlfriend as a "fucking bitch" and said she stole from him.

"I want Manuela out of my life," he said when asked what he wanted at the end of the trial, adding that he wished his daughter Shari to take over as his healthcare agent.

Reporters and the public in attendance were cleared from the courtroom while Mr Redstone's deposition was played back as the trial got underway Friday. A transcript was released afterwards.

Los Angeles Superior Judge David Cowan appeared swayed by Mr Redstone's testimony after viewing the videotape, describing it as "strong evidence". He said he would rule on a defense motion to dismiss the case on Monday.

"Your burden is now a hard one," the judge told Ms Herzer's attorney.

The testimony of Mr Redstone, who has not been seen in public for nearly a year, is sure to be scrutinised closely.

The trial's outcome could have an impact on his US$40 billion media empire, which includes MTV, Comedy Central and Paramount Pictures.

If Mr Redstone is found incompetent, his associates could push for him to be removed as the controlling shareholder of Viacom and CBS, triggering a power struggle across his businesses.

Mr Redstone in February stepped down as executive chairman of CBS, which includes some of the most iconic names in the entertainment business.

Ms Herzer filed her lawsuit claiming Mr Redstone was mentally incompetent when he kicked her out of his home in October and cut her out of his will.

The case has captivated Hollywood and Wall Street as court papers have laid out salacious details about the mogul's private life.

Ms Herzer essentially must prove that Mr Redstone was of sound mind when he appointed her as his healthcare agent in September 2015, but that he lacked the capacity to revoke the directive a month later.

Her attorney Pierce O'Donnell said during opening statements that Mr Redstone's 62-year-old daughter Shari, his nursing staff and others in his entourage had basically staged a "coup" and "brainwashed" him into dumping her.

"His decision was not that of a sound mind," he said.

He added that Mr Redstone's poor health was apparent during his deposition, during which questions had to be repeatedly reformulated and which was briefly interrupted at one point so his dentures could be adjusted.

However, the mogul's attorney Robert Klieger said that while his client may have trouble communicating, he was of sound mind and had decided on his own to remove Ms Herzer as his caregiver.

"He knew exactly what he was doing," Mr Klieger said. "He didn't want her in that position and he removed her.

"He had the capacity to make that decision and he made it of his own free will."

Dr Stephen Read, a geriatric psychiatrist retained by Ms Herzer, testified on Friday that Mr Redstone had "mild to severe dementia" and appeared "severely impaired" when he examined him in January, media reports said.

Dr Read said that the mogul's caregivers play him recorded sports events, making sure his bets always pay off even though he can't identify his team.