All a system like that will do is make people turn down the volume at red lights (if their car is at the crosswalk). If they’re not right up front, the camera won’t be able to see the license plate, therefore, they don’t need to turn the music down.

Once the light turns green, they can crank up the volume and the camera pointing the other way will hear the sound and click a picture of the car on the crossing street and they’ll be cited for noise.

As for the issue with privacy… if you’re in a public place, you have no expectation of privacy, so it’s ok to take your picture (at least according to the law). That’s why they can have cameras at banks, grocery stores, etc.