MainActivity.java

mCameraSource = new CameraSource.Builder(getApplicationContext(), mTextRecognizer)
                    .setFacing(CameraSource.CAMERA_FACING_BACK)
                    .setRequestedPreviewSize(1280, 1024)
                    .setRequestedFps(15.0f)
                    .setAutoFocusEnabled(true)
                    .build();

mSurfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
                @Override
                public void surfaceCreated(SurfaceHolder holder) {
                    if (ActivityCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) {
                        try {
                            mCameraSource.start(mSurfaceView.getHolder());
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    } else {
                        askCameraPermission();
                    }
                }

                @Override
                public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {

                }

                @Override
                public void surfaceDestroyed(SurfaceHolder holder) {
                    mCameraSource.stop();
                }
            });          
    }