How to correctly use ImageReader with YUV_420_888 and MediaCodec to encode video to h264 format?

Question

I'm implementing a camera application on Android devices. Currently, I use Camera2 API and ImageReader to get image data in YUV_420_888 format, but I don't know how to exactly write these data to MediaCodec.

Here are my questions:

1. What is YUV_420_888?

The format YUV_420_888 is ambiguous because it can be any format which belongs to the YUV420 family, such as YUV420P, YUV420PP, YUV420SP and YUV420PSP, right?

By accessing the image's three planes(#0, #1, #2), I can get the Y(#0), U(#1), V(#2) values of this image. But the arrangement of these values may not be the same on different devices. For example, if YUV_420_888 truly means YUV420P, the size of both Plane#1 and Plane#2 is a quarter of the size of Plane#0. If YUV_420_888 truly means YUV420SP, the size of both Plane#1 and Plane#2 is half of the size of Plane#0(Each of Plane#1 and Plane#2 contains U, V values).

If I want to write these data from image's three planes to MediaCodec, what kind of format I need to convert to? YUV420, NV21, NV12, ...?

2. What is COLOR_FormatYUV420Flexible?

The format COLOR_FormatYUV420Flexible is also ambiguous because it can be any format which belongs to the YUV420 family, right? If I set KEY_COLOR_FORMAT option of a MediaCodec object to COLOR_FormatYUV420Flexible, what format(YUV420P, YUV420SP...?) of data should I input to the MediaCodec object?

3. How about using COLOR_FormatSurface?

I know MediaCodec has its own surface, which can be used if I set KEY_COLOR_FORMAT option of a MediaCodec object to COLOR_FormatSurface. And with Camera2 API, I don't need to write any data by myself to the MediaCodec object. I can just drain the output buffer.

However, I need to change the image from the camera. For example, draw other pictures, write some text on it, or insert another video as POP(Picture of Picture).

Can I use ImageReader to read the image from Camera, and after re-drawing that, write the new data to MediaCodec's surface, and then drain it out? How to do that?

EDIT1

I implemented the function by using COLOR_FormatSurface and RenderScript. Here is my code:

onImageAvailable method:

public void onImageAvailable(ImageReader imageReader) {
    try {
        try (Image image = imageReader.acquireLatestImage()) {
            if (image == null) {
                return;
            }
            Image.Plane[] planes = image.getPlanes();
            if (planes.length >= 3) {
                ByteBuffer bufferY = planes[0].getBuffer();
                ByteBuffer bufferU = planes[1].getBuffer();
                ByteBuffer bufferV = planes[2].getBuffer();
                int lengthY = bufferY.remaining();
                int lengthU = bufferU.remaining();
                int lengthV = bufferV.remaining();
                byte[] dataYUV = new byte[lengthY + lengthU + lengthV];
                bufferY.get(dataYUV, 0, lengthY);
                bufferU.get(dataYUV, lengthY, lengthU);
                bufferV.get(dataYUV, lengthY + lengthU, lengthV);
                imageYUV = dataYUV;
            }
        }
    } catch (final Exception ex) {

    }
}

Convert YUV_420_888 to RGB:

public static Bitmap YUV_420_888_toRGBIntrinsics(Context context, int width, int height, byte[] yuv) {
    RenderScript rs = RenderScript.create(context);
    ScriptIntrinsicYuvToRGB yuvToRgbIntrinsic = ScriptIntrinsicYuvToRGB.create(rs, Element.U8_4(rs));

    Type.Builder yuvType = new Type.Builder(rs, Element.U8(rs)).setX(yuv.length);
    Allocation in = Allocation.createTyped(rs, yuvType.create(), Allocation.USAGE_SCRIPT);

    Type.Builder rgbaType = new Type.Builder(rs, Element.RGBA_8888(rs)).setX(width).setY(height);
    Allocation out = Allocation.createTyped(rs, rgbaType.create(), Allocation.USAGE_SCRIPT);


    Bitmap bmpOut = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);

    in.copyFromUnchecked(yuv);

    yuvToRgbIntrinsic.setInput(in);
    yuvToRgbIntrinsic.forEach(out);
    out.copyTo(bmpOut);
    return bmpOut;
}

MediaCodec:

mediaFormat.setInteger(MediaFormat.KEY_COLOR_FORMAT, MediaCodecInfo.CodecCapabilities.COLOR_FormatSurface);
...
mediaCodec.configure(mediaFormat, null, null, MediaCodec.CONFIGURE_FLAG_ENCODE);
...
surface = mediaCodec.createInputSurface(); // This surface is not used in Camera APIv2. Camera APIv2 uses ImageReader's surface.

And in athother thread:

while (!stop) {
    final byte[] image = imageYUV;

    // Do some yuv computation

    Bitmap bitmap = YUV_420_888_toRGBIntrinsics(getApplicationContext(), width, height, image);
    Canvas canvas = surface.lockHardwareCanvas();
    canvas.drawBitmap(bitmap, matrix, paint);
    surface.unlockCanvasAndPost(canvas);
}

This way works, but the performance is not good. It can't output 30fps video files(only ~12fps). Perhaps I should not use COLOR_FormatSurface and the surface's canvas for encoding. The computed YUV data should be written to the mediaCodec directly without any surface doing any conversion. But I still don't know how to do that.

Answer 1

You are right, YUV_420_888 is a format that can wrap different YUV 420 formats. The spec carefully explains that the arrangement of U and V planes is not prescribed, but there are certain restrictions; e.g. if the U plane has pixel stride 2, same applies to V (and then the underlying byte buffer can be NV21).

COLOR_FormatYUV420Flexible is a synonym of YUV_420_888, but they belong to different classes: MediaCodec and ImageFormat, respectively.

The spec explains:

All video codecs support flexible YUV 4:2:0 buffers since LOLLIPOP_MR1.

COLOR_FormatSurface is an opaque format that can deliver best performance for MediaCodec, but this comes at price: you cannot directly read or manipulate its content. If you need to manipulate the data that goes to the MediaCodec, then using ImageReader is an option; whether it will be more efficient than ByteBuffer, depends on what you do and how you do it. Note that for API 24+ you can work with both camera2 and MediaCodec in C++.

The invaluable resource of details for MediaCodec is http://www.bigflake.com/mediacodec. It references a full example of 264 encoding.