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android – Custom byteArray data to WebRTC videoTrack

Posted by: admin May 14, 2020 Leave a comment

Questions:

I need to use WebRTC for android to send specific cropped(face) video to the videoChannel. I was able manipulate Camera1Session class of WebRTC to get the face cropped. Right now I am setting it to an ImageView.
listenForBytebufferFrames() of Camera1Session.java

private void listenForBytebufferFrames() {
    this.camera.setPreviewCallbackWithBuffer(new PreviewCallback() {
        public void onPreviewFrame(byte[] data, Camera callbackCamera) {
            Camera1Session.this.checkIsOnCameraThread();
            if(callbackCamera != Camera1Session.this.camera) {
                Logging.e("Camera1Session", "Callback from a different camera. This should never happen.");
            } else if(Camera1Session.this.state != Camera1Session.SessionState.RUNNING) {
                Logging.d("Camera1Session", "Bytebuffer frame captured but camera is no longer running.");
            } else {
                mFrameProcessor.setNextFrame(data, callbackCamera);
                long captureTimeNs = TimeUnit.MILLISECONDS.toNanos(SystemClock.elapsedRealtime());
                if(!Camera1Session.this.firstFrameReported) {
                    int startTimeMs = (int)TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - Camera1Session.this.constructionTimeNs);
                    Camera1Session.camera1StartTimeMsHistogram.addSample(startTimeMs);
                    Camera1Session.this.firstFrameReported = true;
                }

                ByteBuffer byteBuffer1 = ByteBuffer.wrap(data);
                Frame outputFrame = new Frame.Builder()
                        .setImageData(byteBuffer1,
                                Camera1Session.this.captureFormat.width,
                                Camera1Session.this.captureFormat.height,
                                ImageFormat.NV21)
                        .setTimestampMillis(mFrameProcessor.mPendingTimeMillis)
                        .setId(mFrameProcessor.mPendingFrameId)
                        .setRotation(3)
                        .build();
                int w = outputFrame.getMetadata().getWidth();
                int h = outputFrame.getMetadata().getHeight();
                SparseArray<Face> detectedFaces = mDetector.detect(outputFrame);
                if (detectedFaces.size() > 0) {

                    Face face = detectedFaces.valueAt(0);
                    ByteBuffer byteBufferRaw = outputFrame.getGrayscaleImageData();
                    byte[] byteBuffer = byteBufferRaw.array();
                    YuvImage yuvimage  = new YuvImage(byteBuffer, ImageFormat.NV21, w, h, null);
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();

                    //My crop logic to get face co-ordinates

                    yuvimage.compressToJpeg(new Rect(left, top, right, bottom), 80, baos);
                    final byte[] jpegArray = baos.toByteArray();
                    Bitmap bitmap = BitmapFactory.decodeByteArray(jpegArray, 0, jpegArray.length);

                    Activity currentActivity = getActivity();
                    if (currentActivity instanceof CallActivity) {
                        ((CallActivity) currentActivity).setBitmapToImageView(bitmap); //face on ImageView is set just fine
                    }
                    Camera1Session.this.events.onByteBufferFrameCaptured(Camera1Session.this, data, Camera1Session.this.captureFormat.width, Camera1Session.this.captureFormat.height, Camera1Session.this.getFrameOrientation(), captureTimeNs);
                    Camera1Session.this.camera.addCallbackBuffer(data);
                } else {
                    Camera1Session.this.events.onByteBufferFrameCaptured(Camera1Session.this, data, Camera1Session.this.captureFormat.width, Camera1Session.this.captureFormat.height, Camera1Session.this.getFrameOrientation(), captureTimeNs);
                    Camera1Session.this.camera.addCallbackBuffer(data);
                }

            }
        }
    });
}

jpegArray is the final byteArray that I need to stream via WebRTC, which I tried with something like this:

Camera1Session.this.events.onByteBufferFrameCaptured(Camera1Session.this, jpegArray, (int) face.getWidth(), (int) face.getHeight(), Camera1Session.this.getFrameOrientation(), captureTimeNs);
Camera1Session.this.camera.addCallbackBuffer(jpegArray);

Setting them up like this gives me following error:

../../webrtc/sdk/android/src/jni/androidvideotracksource.cc line 82
Check failed: length >= width * height + 2 * uv_width * ((height + 1) / 2) (2630 vs. 460800)

Which I assume is because androidvideotracksource does not get the same length of byteArray that it expects, since the frame is cropped now.
Could someone point me in the direction of how to achieve it? Is this the correct way/place to manipulate the data and feed into the videoTrack?

Edit:bitmap of byteArray data does not give me a camera preview on ImageView, unlike byteArray jpegArray. Maybe because they are packed differently?

How to&Answers:

Can we use WebRTC’s Datachannel to exchang custom data ie cropped face “image” in your case and do the respective calculation at receiving end using any third party library ie OpenGL etc? Reason I am suggesting is that the WebRTC Video feed received from channel is a stream in real time not a bytearray . WebRTC Video by its inherent architecture isn’t meant to crop video at other hand. If we want to crop or augment video we have to use any ar library to fulfill this job.

We can always leverage WebRTC’s Data channel to exchange customized data. Using Video channel for the same is not recommended because it’s real time stream not the bytearray.Please revert in case of any concern.

Answer:

WebRTC in particular and video streaming in general presumes that the video has fixed dimensions. If you want to crop the detected face, your options are either to have pad the cropped image with e.g. black pixels (WebRTC does not use transparency), and crop the video on the receiver side, or, if you don’t have control over the receiver, resize the cropped region to fill the expected width * height frame (you should also keep the expected aspect ratio).

Note that JPEG compress/decompress that you use to crop the original is far from efficient. Some other options can be found in Image crop and resize in Android.

Answer:

Okay, this was definitely a problem of how the original byte[] data was packed and the way byte[] jpegArray was packed. Changing the way of packing this and scaling it as AlexCohn suggested worked for me. I found help from other post on StackOverflow on way to pack it. This is the code for it:

private byte[] getNV21(int left, int top, int inputWidth, int inputHeight, Bitmap scaled) {
int [] argb = new int[inputWidth * inputHeight];
    scaled.getPixels(argb, 0, inputWidth, left, top, inputWidth, inputHeight);
    byte [] yuv = new byte[inputWidth*inputHeight*3/2];
    encodeYUV420SP(yuv, argb, inputWidth, inputHeight);
    scaled.recycle();
    return yuv;
}

private void encodeYUV420SP(byte[] yuv420sp, int[] argb, int width, int height) {
    final int frameSize = width * height;

    int yIndex = 0;
    int uvIndex = frameSize;

    int a, R, G, B, Y, U, V;
    int index = 0;
    for (int j = 0; j < height; j++) {
        for (int i = 0; i < width; i++) {

            a = (argb[index] & 0xff000000) >> 24; // a is not used obviously
            R = (argb[index] & 0xff0000) >> 16;
            G = (argb[index] & 0xff00) >> 8;
            B = (argb[index] & 0xff) >> 0;

            // well known RGB to YUV algorithm
            Y = ( (  66 * R + 129 * G +  25 * B + 128) >> 8) +  16;
            U = ( ( -38 * R -  74 * G + 112 * B + 128) >> 8) + 128;
            V = ( ( 112 * R -  94 * G -  18 * B + 128) >> 8) + 128;

            // NV21 has a plane of Y and interleaved planes of VU each sampled by a factor of 2
            //    meaning for every 4 Y pixels there are 1 V and 1 U.  Note the sampling is every other
            //    pixel AND every other scanline.
            yuv420sp[yIndex++] = (byte) ((Y < 0) ? 0 : ((Y > 255) ? 255 : Y));
            if (j % 2 == 0 && index % 2 == 0) {
                yuv420sp[uvIndex++] = (byte)((V<0) ? 0 : ((V > 255) ? 255 : V));
                yuv420sp[uvIndex++] = (byte)((U<0) ? 0 : ((U > 255) ? 255 : U));
            }

            index ++;
        }
    }
}`

I pass this byte[] data to onByteBufferFrameCaptured and callback:

Camera1Session.this.events.onByteBufferFrameCaptured(
                            Camera1Session.this,
                            data,
                            w,
                            h,
                            Camera1Session.this.getFrameOrientation(),
                            captureTimeNs);
Camera1Session.this.camera.addCallbackBuffer(data);

Prior to this, I had to scale the bitmap which is pretty straight forward:

int width = bitmapToScale.getWidth();
int height = bitmapToScale.getHeight();
Matrix matrix = new Matrix();
matrix.postScale(newWidth / width, newHeight / height);
Bitmap scaledBitmap = Bitmap.createBitmap(bitmapToScale, 0, 0, bitmapToScale.getWidth(), bitmapToScale.getHeight(), matrix, true);