How to use a custom video capturer and add to local video track with WebRTC for Android (org.webrtc)

I have this custom video capturer class:

...

import org.webrtc.JavaI420Buffer;
import org.webrtc.SurfaceTextureHelper;
import org.webrtc.VideoCapturer;
import org.webrtc.VideoFrame;

import java.nio.ByteBuffer;

public class CustomCapturer implements VideoCapturer {

    private SurfaceTextureHelper surTexture;
    private Context appContext;
    private org.webrtc.CapturerObserver capturerObs;
    private Thread captureThread;

    @Override
    public void initialize(SurfaceTextureHelper surfaceTextureHelper, Context applicationContext, org.webrtc.CapturerObserver capturerObserver) {
        surTexture = surfaceTextureHelper;
        appContext = applicationContext;
        capturerObs = capturerObserver;
    }

    public void addFrame(Bitmap frame_asbitmap) {
        try {
            final long captureTimeNs =
                    TimeUnit.MILLISECONDS.toNanos(SystemClock.elapsedRealtime());
            long start = System.nanoTime();
            JavaI420Buffer buffer = JavaI420Buffer.allocate(640, 480);
            bitmapToI420(frame_asbitmap, buffer);
            long frameTime = System.nanoTime() - start;
            VideoFrame videoFrame = new VideoFrame(buffer, 0, frameTime);
            capturerObs.onFrameCaptured(videoFrame);
        } catch (Exception e) {
        }
    }

    @Override
    public void startCapture(int width, int height, int fps) {
        captureThread = new Thread(() -> {
            try {
                long start = System.nanoTime();
                capturerObs.onCapturerStarted(true);

            } catch(InterruptedException ex) {
                ex.printStackTrace();
            }
        });
        captureThread.start();
    }

    @Override
    public void stopCapture() {
        captureThread.interrupt();
    }

    @Override
    public void changeCaptureFormat(int width, int height, int fps) {
    }

    @Override
    public void dispose() {    }

    @Override
    public boolean isScreencast() {
        return false;
    }
}

How to use this as a source for the local video track? I have looked for documentation on this but could not find any. I plan to attach this class to the local video track and then add frames to it form a USB camera using the addFrame(Bitmap frame_asbitmap) method from MainActivity.