From the OpenCV documentation:
The 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:show_fps="true" and opencv:camera_id="any" options enable FPS message and allow to use any camera on device. Application tries to use back camera first.
Implementation of 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.
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