public void setRequestedCameraId(int requestedCameraId) {
        this.requestedCameraId = requestedCameraId;
    }
Allows third party apps to specify the camera ID, rather than determine
it automatically based on available cameras and their orientation.

@param requestedCameraId camera ID of the camera to use. A negative value means "no preference".
zxing-android-embedded/src/com/journeyapps/barcodescanner/camera/CameraSettings.java