void RTSPFFmpeg::rtsp_open(const char *url) {

    AVFormatContext* format_ctx = avformat_alloc_context();

    AVCodecContext *pAVCodecContext_video = nullptr;

    AVCodec *pAVCodec_video = nullptr;

    AVCodecParameters *pAVCodePar_video = avcodec_parameters_alloc();

    AVPacket *pAVPacket = av_packet_alloc(); ;                                  // ffmpeg单帧数据包

    AVFrame *pAVFrame_video = av_frame_alloc();                                 // ffmpeg单帧缓存

    AVFrame *pAVFrameRGB32_video = av_frame_alloc();                            // ffmpeg单帧缓存转换颜色空间后的缓存

    AVCodecParserContext *pAVCodeParseContext_video = nullptr;

    struct SwsContext *pSwsContext_video = nullptr;                             // ffmpeg编码数据格式转换

    AVDictionary * opts = nullptr;

    int ret = -1;

    int numBytes = 0;                                                           // 解码后的数据长度

    u_char *outBuffer = nullptr;                                                // 解码后的数据存放缓存区

 // open rtsp: Open an input stream and read the header. The codecs are not opened

    //const char* url = "rtsp://admin:genepoint2020@192.168.100.14:554/cam/realmonitor?channel=1&subtype=0";

    av_dict_set(&opts, "rtsp_transport", "tcp", 0);

    av_dict_set(&opts, "stimeout", "2000000", 0);

    // audio/video stream index

    int video_stream_index = -1;

　　 ret = avformat_open_input(&format_ctx, url, nullptr, &opts);

        if (ret != 0) {

            fprintf(stderr, "fail to open url: %s, return value: %d\n", url, ret);

continue;

        }

        // Read packets of a media file to get stream information

        ret = avformat_find_stream_info(format_ctx, nullptr);

        if (ret < 0) {

            fprintf(stderr, "fail to get stream information: %d\n", ret);

continue;

        }

        fprintf(stdout, "Number of elements in AVFormatContext.streams: %d\n", format_ctx->nb_streams);

        for (int i = 0; i < format_ctx->nb_streams; ++i) {

            const AVStream *stream = format_ctx->streams[i];

            fprintf(stdout, "type of the encoded data: %d\n", stream->codecpar->codec_id);

            if (stream->codecpar->codec_type == AVMEDIA_TYPE_VIDEO) {

                video_stream_index = i;

                // 对找到的视频流寻解码器

                pAVCodePar_video = stream->codecpar;

                pAVCodec_video = avcodec_find_decoder(stream->codecpar->codec_id);

                if (!pAVCodec_video) {

                    video_stream_index = -1;

                    break;

                }

                pAVCodeParseContext_video = av_parser_init(pAVCodec_video->id);

                if (!pAVCodeParseContext_video) {

                    video_stream_index = -1;

                    break;

                }

                pAVCodecContext_video = avcodec_alloc_context3(pAVCodec_video);

                if (!pAVCodecContext_video) {

                }

                if (avcodec_open2(pAVCodecContext_video, pAVCodec_video, NULL) < 0) {

                    video_stream_index = -1;

                    break;

                }

                fprintf(stdout, "dimensions of the video frame in pixels: width: %d, height: %d, pixel format: %d\n",

                        stream->codecpar->width, stream->codecpar->height, stream->codecpar->format);

            }

        }

        if (video_stream_index == -1) {

            fprintf(stderr, "no video stream\n");

continue;

        }

        // 对拿到的原始数据格式进行缩放转换为指定的格式高宽大小

        pSwsContext_video = sws_getContext(

                pAVCodePar_video->width,

                pAVCodePar_video->height,

                static_cast<AVPixelFormat>(pAVCodePar_video->format),

                pAVCodePar_video->width,

                pAVCodePar_video->height,

                AV_PIX_FMT_RGBA,

                SWS_FAST_BILINEAR,

                nullptr,

                nullptr,

                nullptr

        );

        numBytes = av_image_get_buffer_size(

                AV_PIX_FMT_RGBA,

                pAVCodePar_video->width,

                pAVCodePar_video->height,

                1

        );

        outBuffer = (u_char *) av_malloc(numBytes);

        // pAVFrame32的data指针指向了outBuffer

        av_image_fill_arrays(

                pAVFrameRGB32_video->data,

                pAVFrameRGB32_video->linesize,

                outBuffer,

                AV_PIX_FMT_RGBA,

                pAVCodePar_video->width,

                pAVCodePar_video->height,

                1

        );

 while (1) {

        ret = av_read_frame(format_ctx, pAVPacket);

        if (ret < 0) {

            fprintf(stderr, "error or end of file: %d\n", ret);

continue;

        }

        if (pAVPacket->stream_index == video_stream_index) {

//            fprintf(stdout, "video stream, packet size: %d\n", pAVPacket->size);

            ret = avcodec_send_packet(pAVCodecContext_video,pAVPacket);

            if( 0 != ret){

continue;

            }

while (avcodec_receive_frame(pAVCodecContext_video,pAVFrame_video) == 0){

                sws_scale(pSwsContext_video,

                          (const uint8_t * const *)pAVFrame_video->data,

                          pAVFrame_video->linesize,

                          0,

                          pAVCodePar_video->height,

                          pAVFrameRGB32_video->data,

                          pAVFrameRGB32_video->linesize);

                QImage image((u_char*)outBuffer,pAVCodePar_video->width,pAVCodePar_video->height,QImage::Format_RGBA8888);

                emit rtsp_image_sig(image);

            }

        }

        av_packet_unref(pAVPacket);

    }

    av_parser_close(pAVCodeParseContext_video);

    av_frame_free(&pAVFrame_video);

    av_frame_free(&pAVFrameRGB32_video);

    av_free(outBuffer);

    av_free(pSwsContext_video);

    avcodec_free_context(&pAVCodecContext_video);

    avformat_close_input(&format_ctx);

}