Lip reading is hardly an exact science. Jeremy Freeman, 49, who has been called upon as an expert lip reader in cases involving sexual assault, insurance fraud and other serious matters, described it as a skill that can be honed with considerable practice. For Mr. Freeman, who was born deaf, the practice has “been ingrained in me since I was brought up,” he said.

He said he still relies on other cues, like body language and social context, to determine what is being said. “There is guessing involved,” said Mr. Freeman, who works as a writer near London. “I would never say I can lip read 100 percent accurately.” Certain people, like the Scottish comedian and actor Billy Connolly, confound him. “I find him impossible to lip read,” Mr. Freeman said.

Aside from accuracy, there is the question of ethics. Is lip reading an invasion of privacy?

Mr. Freeman said he would never lip read someone in their home. But if it’s a celebrity at a live event, like the coronation of King Charles III, which he lip read for a media outlet, he views it as “part of the commentary.” (He added that he heard from a deaf person afterward who thought that it was an invasion of privacy.)

Ms. Dellinger said she also has limits. In a video she posted on a conversation between Olivia Rodrigo and Iris Apatow in the front row of a Los Angeles Lakers game, Ms. Dellinger left out the name of the person Ms. Rodrigo appeared to say she was dating.

Krystin Kalvoy, 25, another popular lip reader on TikTok, said she will not interpret videos in which she believes something deeply personal is being said. She recently lip read footage of royal family members during the coronation, after having decided against trying to narrate what the Afflecks were saying at the Grammys, which some TikTok users had asked her to do.

“The last thing I would want is to leak private moments,” said Ms. Kalvoy, who is hearing-impaired. ‘We want to know what’s going on? Is Ben drinking again?’ You don’t want to be the fuel to that fire.”