How to convert OpenCV's Mat format to FFMPEG's avframe format?

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I made the conversion between FFmpeg's avframe and OpenCV's mat. But the following code doesn't convert the avframe to mat and mat to avframe correctly. The first part converts avframe to mat format and the second part converts mat to avframe format.

Here is my source code:

 AVFrame* ProcessFrame(AVFrame *frame, int stream_index)
{
 //first part
    AVStream *in_stream = ifmt_ctx->streams[stream_index];
    AVCodecContext *pCodecCtx = in_stream->codec;

    AVFrame  *pFrameRGB = NULL;

    struct SwsContext * img_convert_ctx = NULL;
    if(img_convert_ctx == NULL){
        img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
                                         pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height,
                                         AV_PIX_FMT_BGR24, SWS_BICUBIC, NULL, NULL, NULL);
    }
    pFrameRGB = av_frame_alloc();
    int size = avpicture_get_size(AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);

    uint8_t  *out_bufferRGB = (uint8_t *)av_malloc(size);

    avpicture_fill((AVPicture *)pFrameRGB, out_bufferRGB, AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);

    sws_scale(img_convert_ctx, frame->data, frame->linesize, 0, pCodecCtx->height, pFrameRGB->data, pFrameRGB->linesize);

    Mat imageFrame = Mat(pCodecCtx->height, pCodecCtx->width, CV_8UC3);

    memcpy(imageFrame.data, out_bufferRGB, size);
    delete[] out_bufferRGB;

   ///////////////////////////////////////////////////////////
   //second part starts

    avpicture_fill((AVPicture *)pFrameRGB, imageFrame.data,AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height);

    struct SwsContext * convert_ctx = NULL;
    if(convert_ctx == NULL){
        convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height,
                                         AV_PIX_FMT_BGR24, pCodecCtx->width, pCodecCtx->height,
                                         pCodecCtx->pix_fmt, SWS_BICUBIC, NULL, NULL, NULL);
    }

    AVFrame *srcFrame = av_frame_alloc();
    size = avpicture_get_size(pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);

    uint8_t  *out_buffer = (uint8_t *)av_malloc(size);

    avpicture_fill((AVPicture *)srcFrame, out_buffer, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height);

    sws_scale(convert_ctx, pFrameRGB->data, pFrameRGB->linesize, 0, pCodecCtx->height, srcFrame->data, srcFrame->linesize);

    delete[] out_buffer;
    av_free(pFrameRGB);

    srcFrame->width = frame->width;
    srcFrame->height = frame->height;
    srcFrame->format = frame->format;

    av_frame_copy_props(srcFrame, frame);

    return srcFrame;
}