I'm not too keen on that. They should have some privacy when they aren't interacting with the public. Nobody wants to be taped while they are eating, or discussing things with a colleague. And the more unpleasant it is to be a police officer, the worse officers you'll get.

However, they should monitor themselves (with video) whenever they are interacting with the public. This helps them gather solid evidence. If they "forgot" to turn on the camera, or "lost" the disk, the judge and jury should be asking why.