Openh264 DecodeFrameNoDelay output buffer yuv is yuv420 format?

Question

I decode h264 file with DecodeFrameNoDelay function and get yuvData buffer

I want write the yuvData buffer to file .yuv and play with ffmpeg command. But when I play yuv file with ffmpeg command the result is not correct.

This is ffmpeg command I use to play yuv file:

ffplay -f rawvideo -pix_fmt yuv420p -video_size 1280x720 input_video.yuv 

This is my code use to decode h264 file and write yuvData buffer to file .yuv

void init(int width, int height) {
    WelsCreateDecoder(&decoder);
    decodingParam = {0};
    decodingParam.sVideoProperty.eVideoBsType = VIDEO_BITSTREAM_AVC;
    decoder->Initialize(&decodingParam);
    bufferInfo = {0};
    bufferInfo.iBufferStatus = 1;

    yuvData = new uint8_t*[3];
    yuvData[0] = new uint8_t[width * height];
    yuvData[1] = new uint8_t[width * height / 4];
    yuvData[2] = new uint8_t[width * height / 4];

}

bool decode(const unsigned char* rawEncodedData, int rawEncodedDataLength, uint8_t** yuvData, char *name) {
    int err = decoder->DecodeFrameNoDelay(rawEncodedData, rawEncodedDataLength, yuvData, &bufferInfo);

    int width = bufferInfo.UsrData.sSystemBuffer.iWidth;
    int height = bufferInfo.UsrData.sSystemBuffer.iHeight;

    FILE *pFile = fopen(std::string("screen.yuv").c_str(), "ab");
    fwrite(yuvData[0], 1, width * height, pFile);
    fwrite(yuvData[1], 1, width * height / 4, pFile);
    fwrite(yuvData[2], 1, width * height / 4, pFile);
    fclose(pFile);

    std::cout << width << height << std::endl;

    if (err != 0) {
        std::cout << "H264 decoding failed. Error code: " << err << "." << std::endl;
        parseErrorCode(err);
        return false;
    }

    printf("H264 decoding success, err: %d, name: %s, status: %d\n", err, name, bufferInfo.iBufferStatus);

    return true;
}

I have some question need make clear:

1/yuvData buffer I get from DecodeFrameNoDelay function is really yuv420 format ?

2/Something wrong with my code ?

Any help is appreciated.

Thanks and best regards.