New York City's police commissioner has unveiled body cameras that his department will start testing soon, demonstrating the equipment by playing a short video showing a good-natured traffic stop from an officer's perspective.

“I’m going to issue you a summons for that red light, okay?” the unseen officer can be heard politely telling the driver he has just pulled over. “Give me a second, okay?” the officer adds in a reassuring voice, which the driver appears to think is fair enough. “I’ll be right back.”

It is the sort of genteel encounter between an officer and a civilian that Bill Bratton, the city's police commissioner since January, has said he hopes would be more common if both parties know they are being recorded.

Other departments already using the cameras have found they tend to bring out the best behaviour on both sides and “de-escalate” encounters with police, Mr Bratton said.

“I think clearly the officer, knowing they are being recorded, will affect the behaviour of the officer in a good way,” he added. Only 60 of the city’s 35,000 officers will be asked to volunteer to wear the cameras in the pilot programme.

The death of Michael Brown, the unarmed Missouri teenager shot by a police officer in disputed circumstances last month, has brought renewed attention to the technology. The officer who shot Brown was not wearing a camera.– (Reuters)