CustomCapturer.java

package it.inrebus.skyte.rtcclient;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.opengl.GLES20;
import android.opengl.GLUtils;

import org.webrtc.SurfaceTextureHelper;
import org.webrtc.TextureBufferImpl;
import org.webrtc.VideoCapturer;
import org.webrtc.VideoFrame;
import org.webrtc.YuvConverter;

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;
    }

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

                int[] textures = new int[1];
                GLES20.glGenTextures(1, textures, 0);

                YuvConverter yuvConverter = new YuvConverter();
                TextureBufferImpl buffer = new TextureBufferImpl(width, height, VideoFrame.TextureBuffer.Type.RGB, textures[0], new Matrix(), surTexture.getHandler(), yuvConverter, null);
                Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);

                while (true) {
                    Canvas canvas = new Canvas(bitmap);
                    canvas.drawRGB(255, 255, 255);
                    Paint paint = new Paint();
                    paint.setColor(Color.RED);
                    paint.setAlpha(0xff);
                    canvas.drawRect(100, 100, 200, 200, paint);

                    surTexture.getHandler().post(() -> {
                        GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_NEAREST);
                        GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_NEAREST);
                        GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);

                        VideoFrame.I420Buffer i420Buf = yuvConverter.convert(buffer);

                        long frameTime = System.nanoTime() - start;
                        VideoFrame videoFrame = new VideoFrame(i420Buf, 0, frameTime);
                        capturerObs.onFrameCaptured(videoFrame);
                    });

                    Thread.sleep(100);
                }
            } 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;
    }
}

I want to do the same thing with you. I want to transmit video data of UAV through webrtc. Can I use this method?

It works.
But should release videoFrame object after used, otherwise it will cause memory leak

Note: OpenGL has a flipped y-coordinate system compared to Android bitmaps. Will need to pass the matrix with scale to 1,-1 to correct for this.

I tried this out, but had some additional issues with tearing and framerate. I ended up using the SurfaceTextureHelper passed in initialize to draw bitmaps to its SurfaceTexture, and it'll convert it for you.