What are the two barrels on the police car?

That's a signal detector. There are antennas, satellite receivers, searchlights, cameras and periscope. Mobile command vehicles (emergency communication command vehicles) and field survey vehicles are generally used. There are also some cameras, speedometers, LED large-screen searchlights, and many kinds.

It seems to be used for shooting on duty as evidence. Just like the police have to wear photography and recording equipment on duty now.

It is generally used for emergency on-site command and processing, and the images can be saved locally or transmitted to the command center.