I have a dash camera that is a no name from Amazon. I think the memory card costs as much as the unit. It has GPS tracking for later reference when you take the memory chip out and plug into a PC. Formatting the chip puts the software on the chip to view the stored data. Manual was useless.
Mine has forward and passenger compartment video recording and voice. I have mine set up with no voice and forward record only. In my state it is illegal to record voice without permission. Video is ok.
I have used it twice to help PD. One was a police takedown in the street that happened in front of me. The cruiser camera was off on one and the other was facing the wrong way. The person taken down was claiming abuse and there was none. The other was a motor vehicle accident where the vehicle just drove into the guardrail with no brakes.
There are many types, with features and quality. You get what you pay for.
Brent