int VideoTest::convert_first_frame_to_png(const char* inputVideoFileName, const char*
outputPngName)
{
    av_register_all();
    avcodec_register_all();
    avformat_network_init();
    av_log_set_level(AV_LOG_DEBUG); // debugging info

    ::AVFormatContext * ctx = NULL;
    int err = avformat_open_input(&ctx, inputVideoFileName, NULL, NULL);
    CHECK_ERR(err);
    err = av_find_stream_info(ctx);
    CHECK_ERR(err);

    AVCodec * codec = NULL;
    int strm = av_find_best_stream(ctx, AVMEDIA_TYPE_VIDEO, -1, -1, &codec, 0);

    AVCodecContext * codecCtx = ctx->streams[strm]->codec;
    err = avcodec_open2(codecCtx, codec, NULL);
    CHECK_ERR(err);

    SwsContext * swCtx = sws_getContext(
        codecCtx->width,
        codecCtx->height,
        codecCtx->pix_fmt,
        640,
        480,
        PIX_OUT_FORMAT,
        SWS_FAST_BILINEAR, 0, 0, 0);

    for (;;)
    {
        AVPacket pkt;
        err = av_read_frame(ctx, &pkt);
        CHECK_ERR(err);

        if (pkt.stream_index == strm)
        {
            int got = 0;
            AVFrame * frame = avcodec_alloc_frame();
            err = avcodec_decode_video2(codecCtx, frame, &got, &pkt);
            CHECK_ERR(err);

            if (got)
            {
                AVFrame * rgbFrame = avcodec_alloc_frame();
                avpicture_alloc((AVPicture *)rgbFrame, PIX_OUT_FORMAT, 640, 480);
                sws_scale(swCtx, frame->data, frame->linesize, 0, frame->height, rgbFrame->data, rgbFrame->linesize);

                AVCodec *outCodec = avcodec_find_encoder(AV_CODEC_ID_PNG);
                AVCodecContext *outCodecCtx = avcodec_alloc_context3(outCodec);
                outCodecCtx->width = 640;
                outCodecCtx->height = 480;
                outCodecCtx->pix_fmt = PIX_OUT_FORMAT;
                outCodecCtx->codec_type = AVMEDIA_TYPE_VIDEO;
                outCodecCtx->time_base.num = codecCtx->time_base.num;
                outCodecCtx->time_base.den = codecCtx->time_base.den;
                CheckResult("Open PNG codec", avcodec_open2(outCodecCtx, outCodec, NULL));

                if (!outCodec) return -1;
                int res = avcodec_open2(outCodecCtx, outCodec, NULL);
                if (res < 0) return -1;

                AVPacket outPacket;
                av_init_packet(&outPacket);
                outPacket.size = 0;
                outPacket.data = NULL;
                int gotFrame = 0;
                int ret = avcodec_encode_video2(outCodecCtx, &outPacket, rgbFrame, &gotFrame);
                if (ret >= 0 && gotFrame)
                {
                    FILE * outPng = fopen(outputPngName, "wb");
                    fwrite(outPacket.data, outPacket.size, 1, outPng);
                    fclose(outPng);
                }

                avcodec_close(outCodecCtx);
                av_free(outCodecCtx);

                break;
            }
            avcodec_free_frame(&frame);
        }
    }
    avformat_network_deinit();
}