Android org.webrtc.VideoRenderer.I420Frame arrays to PreviewCallback.onPreviewFrame byte[]

Question

I keep hoping some code will appear on the internet, but getting nowhere ;)

WebRTC incoming I420Frame object seems to have 3 arrays of yuvPlanes

A typical An

Answer 1

While the question is pretty old, I'm posting this answer for anyone who need to do this conversion. I found the below code in one of the WebRTC test cases, and it works perfectly.

 private void testI420toNV21Conversion(ImageView iv) {
    // create a test I420 frame. Instead of this you can use the actual frame
    VideoFrame.I420Buffer i420Buffer = createTestI420Buffer();

    final int width = i420Buffer.getWidth();
    final int height = i420Buffer.getHeight();
    //convert to nv21, this is the same as byte[] from onPreviewCallback
    byte[] nv21Data = createNV21Data(i420Buffer);

    //let's test the conversion by converting the NV21 data to jpg and showing it in a bitmap.
    YuvImage yuvImage = new YuvImage(nv21Data, ImageFormat.NV21,width,height,null);
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    yuvImage.compressToJpeg(new Rect(0, 0, width, height), 100, out);
    byte[] imageBytes = out.toByteArray();
    Bitmap image = BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.length);
    iv.setImageBitmap(image);
}

.

/** Create an NV21Buffer with the same pixel content as the given I420 buffer. **/
public static byte[] createNV21Data(VideoFrame.I420Buffer i420Buffer) {
    final int width = i420Buffer.getWidth();
    final int height = i420Buffer.getHeight();
    final int chromaStride = width;
    final int chromaWidth = (width + 1) / 2;
    final int chromaHeight = (height + 1) / 2;
    final int ySize = width * height;
    final ByteBuffer nv21Buffer = ByteBuffer.allocateDirect(ySize + chromaStride * chromaHeight);
    // We don't care what the array offset is since we only want an array that is direct.
    @SuppressWarnings("ByteBufferBackingArray") final byte[] nv21Data = nv21Buffer.array();
    for (int y = 0; y < height; ++y) {
        for (int x = 0; x < width; ++x) {
            final byte yValue = i420Buffer.getDataY().get(y * i420Buffer.getStrideY() + x);
            nv21Data[y * width + x] = yValue;
        }
    }
    for (int y = 0; y < chromaHeight; ++y) {
        for (int x = 0; x < chromaWidth; ++x) {
            final byte uValue = i420Buffer.getDataU().get(y * i420Buffer.getStrideU() + x);
            final byte vValue = i420Buffer.getDataV().get(y * i420Buffer.getStrideV() + x);
            nv21Data[ySize + y * chromaStride + 2 * x + 0] = vValue;
            nv21Data[ySize + y * chromaStride + 2 * x + 1] = uValue;
        }
    }
    return nv21Data;
}

/** Convert a byte array to a direct ByteBuffer. */
private static ByteBuffer toByteBuffer(int[] array) {
    final ByteBuffer buffer = ByteBuffer.allocateDirect(array.length);
    buffer.put(toByteArray(array));
    buffer.rewind();
    return buffer;
}


/**
 * Convert an int array to a byte array and make sure the values are within the range [0, 255].
 */
private static byte[] toByteArray(int[] array) {
    final byte[] res = new byte[array.length];
    for (int i = 0; i < array.length; ++i) {
        final int value = array[i];
        res[i] = (byte) value;
    }
    return res;
}


public static VideoFrame.I420Buffer createTestI420Buffer() {
    final int width = 16;
    final int height = 16;
    final int[] yData = new int[] {156, 162, 167, 172, 177, 182, 187, 193, 199, 203, 209, 214, 219,
            224, 229, 235, 147, 152, 157, 162, 168, 173, 178, 183, 188, 193, 199, 205, 210, 215, 220,
            225, 138, 143, 148, 153, 158, 163, 168, 174, 180, 184, 190, 195, 200, 205, 211, 216, 128,
            133, 138, 144, 149, 154, 159, 165, 170, 175, 181, 186, 191, 196, 201, 206, 119, 124, 129,
            134, 140, 145, 150, 156, 161, 166, 171, 176, 181, 187, 192, 197, 109, 114, 119, 126, 130,
            136, 141, 146, 151, 156, 162, 167, 172, 177, 182, 187, 101, 105, 111, 116, 121, 126, 132,
            137, 142, 147, 152, 157, 162, 168, 173, 178, 90, 96, 101, 107, 112, 117, 122, 127, 132, 138,
            143, 148, 153, 158, 163, 168, 82, 87, 92, 97, 102, 107, 113, 118, 123, 128, 133, 138, 144,
            149, 154, 159, 72, 77, 83, 88, 93, 98, 103, 108, 113, 119, 124, 129, 134, 139, 144, 150, 63,
            68, 73, 78, 83, 89, 94, 99, 104, 109, 114, 119, 125, 130, 135, 140, 53, 58, 64, 69, 74, 79,
            84, 89, 95, 100, 105, 110, 115, 120, 126, 131, 44, 49, 54, 59, 64, 70, 75, 80, 85, 90, 95,
            101, 106, 111, 116, 121, 34, 40, 45, 50, 55, 60, 65, 71, 76, 81, 86, 91, 96, 101, 107, 113,
            25, 30, 35, 40, 46, 51, 56, 61, 66, 71, 77, 82, 87, 92, 98, 103, 16, 21, 26, 31, 36, 41, 46,
            52, 57, 62, 67, 72, 77, 83, 89, 94};
    final int[] uData = new int[] {110, 113, 116, 118, 120, 123, 125, 128, 113, 116, 118, 120, 123,
            125, 128, 130, 116, 118, 120, 123, 125, 128, 130, 132, 118, 120, 123, 125, 128, 130, 132,
            135, 120, 123, 125, 128, 130, 132, 135, 138, 123, 125, 128, 130, 132, 135, 138, 139, 125,
            128, 130, 132, 135, 138, 139, 142, 128, 130, 132, 135, 138, 139, 142, 145};
    final int[] vData = new int[] {31, 45, 59, 73, 87, 100, 114, 127, 45, 59, 73, 87, 100, 114, 128,
            141, 59, 73, 87, 100, 114, 127, 141, 155, 73, 87, 100, 114, 127, 141, 155, 168, 87, 100,
            114, 128, 141, 155, 168, 182, 100, 114, 128, 141, 155, 168, 182, 197, 114, 127, 141, 155,
            168, 182, 196, 210, 127, 141, 155, 168, 182, 196, 210, 224};
    return JavaI420Buffer.wrap(width, height, toByteBuffer(yData),
            /* strideY= */ width, toByteBuffer(uData), /* strideU= */ width / 2, toByteBuffer(vData),
            /* strideV= */ width / 2,
            /* releaseCallback= */ null);
}