-- record audio and video
-- upload it on-the-fly (as it is being recorded) automatically
-- keep recording when the phone is locked or otherwise off/inaccessible to others, as it may be taken away from you
Openwatch meets 1 of those requirements. Still waiting for something that meets all 3...
I question just how anonymous a recording of your interaction with the police can be made. Surely the officers in question will recognize recordings of themselves and have records of just who all they pulled over that day?
Say for example, you caught me killing a puppy with your camera phone. I'm your neighbour so you post the picture online with a hint to location via an anonymous account through many proxies. There's newspaper frontpage outrage and I'm outraged. I investigate and look at the picture file. Lo and behold, I recognise the camera make as yours and know who it is. So it's not only police that you want to protect yourself from.
Disclaimer: I like puppies though :(
That's the thing... you want it to. If you're pulled over by the police you want to 1) start recording, 2) start uploading to a server in some other jurisdiction 3) Lock your phone so that police can't see that it's recording/uploading, 4) the power-off button is disabled.
A police officer noticing your phone during an arrest and clicking on "stop recording" is a totally different situation than him asking you for your password.