Everyone from President Barack Obama to Mayor Bill de Blasio to NYPD Commissioner William Bratton has touted the idea of camera-wearing cops, and they're right -- the high concept is great.

Body cams have the potential to provide the public with instant replays of controversial cop-citizen confrontations -- perhaps bringing a revolutionary new element of clarity and accountability to police-community relations.

Right now the NYPD is putting 54 camera-wearing cops on the streets in a test program -- to figure out what works and what needs fine-tuning.

What are they likely to find?

Cameras alone won't build trust. Eric Garner died at police hands in an incident that was video-recorded on a bystander's cellphone. And the officer accused in his death, Daniel Pantaleo, was seen waving at the lens as Garner lay dying. But with the ramped-up training the NYPD is giving to 22,000 patrol officers, official police video is likely to be given more consideration when considered by jurors or when it's a citizen's story against officialdom.

Privacy is a major question.When is it best for a camera to go on? Presumably when an encounter is leading to an arrest. What if a cop hits the off switch at a crucial moment? If the purpose is to evade accountability, then disciplinary action might be in order. Will NYPD recordings be subject to freedom-of-information requests? We hope so. And will privacy be safeguarded to the extent possible in domestic violence cases and the like? It should be.

How long will recordings be kept? One answer is to keep them until the statute of limitations expires for filing a claim against the NYPD, but they should be kept indefinitely if the video was evidence in a disciplinary proceeding against a cop. The city is worried about storage issues. But 1 in 6 police agencies nationally uses this technology. While the NYPD is the largest police department in the country, the issue of storage should not be a deal-breaker.

New technology that serves old habits solves nothing. But a confrontation recorded by a cop who's following the rules could be a godsend. Conversely, in a tainted arrest, it could help the accused. On balance, the idea is a keeper.