opencv - How to use Android Camera in Background?

Question

I'm currently developing an app which need to record video in background and process it.

(It needs to get camera preview data real-time in background and have to image process the preview data)

However, to achieve it, I need to use Camera and OpenCV as Service, and it seems that it is impossible to use JavaCameraView in OpenCV and Android.Hardware.Camera without using any preview.

Here are my questions.

1. I heard that NativeCamera in OpenCV can be used for this purpose. Is it possible? (Possibly with examples?)

2. Is there any method that I can use JavaCameraView(or similar stuff) for this purpose? I currently use Galaxy S4.

3. Is there any possible workarounds if android doesn't support such method?(Using Camera Preview without any surface view, or Process camera data without using preview)

4. (OPTIONAL)Why the android doesn't support such operation? It is very annoying!

Thank you for answering the question.

Answer 1

Yes it is possible with following steps..

Create one activity which will start your background service on some event or you can also use alarm manager to start and stop the service as per your requirement.

See the below code that'll help you.

public boolean starMediaRecording(){
        Camera.Parameters params = mServiceCamera.getParameters();
        mServiceCamera.setParameters(params);
        Camera.Parameters p = mServiceCamera.getParameters();

        final List<Size> listSize = p.getSupportedPreviewSizes();
        Size mPreviewSize = listSize.get(2);
        p.setPreviewSize(mPreviewSize.width, mPreviewSize.height);
        p.setPreviewFormat(PixelFormat.YCbCr_420_SP);
        mServiceCamera.setParameters(p);

        try {
            mServiceCamera.setPreviewDisplay(mSurfaceHolder);
            mServiceCamera.startPreview();
        }
        catch (IOException e) {
            Log.e(TAG, e.getMessage());
            e.printStackTrace();
        }

        mServiceCamera.unlock();

        mMediaRecorder = new MediaRecorder();
        mMediaRecorder.setCamera(mServiceCamera);
        mMediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        mMediaRecorder.setVideoSource(MediaRecorder.VideoSource.CAMERA);
        mMediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
        mMediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.DEFAULT);
        mMediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.DEFAULT);
        mMediaRecorder.setOutputFile("/sdcard/filenamevideo.mp4");
        mMediaRecorder.setVideoFrameRate(30);
        mMediaRecorder.setVideoSize(mPreviewSize.width, mPreviewSize.height);
        mMediaRecorder.setPreviewDisplay(mSurfaceHolder.getSurface());

        mMediaRecorder.prepare();
        mMediaRecorder.start(); 

        mRecordingStatus = true;

        return true;

}

public void stopMediaRecorder() {
    mServiceCamera.reconnect();

    mMediaRecorder.stop();
    mMediaRecorder.reset();

    mServiceCamera.stopPreview();
    mMediaRecorder.release();

    mServiceCamera.release();
    mServiceCamera = null;
    }
}