From the OpenCV documentation:
org.opencv.android.JavaCameraView class is implemented inside OpenCV library. It is inherited from
CameraBridgeViewBase, that extends
SurfaceView and uses standard Android camera API. Alternatively you can use
org.opencv.android.NativeCameraView class, that implements the same interface, but uses
VideoCapture class as camera access back-end.
opencv:camera_id="any" options enable FPS message and allow to use any camera on device. Application tries to use back camera first.
CvCameraViewListener interface allows you to add processing steps after frame grabbing from camera and before its rendering on screen. The most important function is
onCameraFrame. It is callback function and it is called on retrieving frame from camera. The callback input is object of
CvCameraViewFrame class that represents frame from camera.