Originally Posted by ican3d

Only certain high end googles have motion "gyro" that controls pan-tilt but for those goggle that doesn't have any can buy add-on external gyro sensor.

Trainer port always exist on any R/C grade radio. If you wanted to learn how to fly R/C on computer simulator you always hook computer USB to radio controller back end port to communicate and control the simulator. That connection part is the "trainer port". Instead connecting to computer the port can be connected to fpv video goggle that have gyro sensor to send CH7/CH8 signal from radio controller to radio receiver then to servo that moves the camera.