Hello, I would like to power my FPV vtx-camera from the car's battery but the vtx works at 3.5-5.5 v. The ESC gives 5v to the receiver so I was wandering if I can take this power for my build. The amps needed are 100-350mA depending on the camera. Our cars HPI Sprint 2 and Kyosho TF-5 have stock electronics. Thanks in advance.
(If you need more info please tell me)

Look in the specs for your ESC, it should tell you the BEC current output of the ESC. Also look at the specs of your servo & reciever, they may say how much current is required by each. If your ESC is specced to handle more than the total power of the Rx + Servo plus the 350mA of the camera there should be no problem, just a case of making up the right cables.

Thank you for the reply, I tried to find these information in the manual but I couldn't. In the end I'm thinking about trying it out , is there a possibility something is gonna take harm ? Or just the camera will not work?

If you have an open slot on receiver you should be able to solder a lead to the camera and plug into receiver. If not a Y harness will do