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ffmpeg接收视频流的时候 初始化经常失败导致再次上线需要花很长时间

连接视频初始化失败会报如下错误：

Could not find codec parameters for stream 0 (Video: h264, none): unspecified size
Consider increasing the value for the 'analyzeduration' and 'probesize' options

结合

https://www.jianshu.com/p/37d705aa0e01

和我们自己的业务做了一些修改

首先修改了probesize的大小，把它调整大了，我担心高清的视频会出现获取不全的情况；

其次修改了analyzeduration的值 由之前1秒设置为5秒钟

另外还新增了一些优化参数

int StreamInputCache::Init(const ProcessRecord& pr) {
	_pFormatCtx = avformat_alloc_context();

	_aviobuffer = (unsigned char*)av_malloc(_buffer_len);
	if (_aviobuffer == 0) {
		dzlog_info("Couldn't open input stream.\n");
		return -1;
	}

	//add by wupengf 2021-03-24 解决累积延迟问题
	_pFormatCtx->probesize = 10000000;//5 000 000
	_pFormatCtx->flags |= AVFMT_FLAG_NOBUFFER;
	av_opt_set(_pFormatCtx->priv_data,"preset","ultrafast",0);

	//AV_TIME_BASE = 1000 000
	_pFormatCtx->max_analyze_duration = 5 * AV_TIME_BASE;
	_pFormatCtx->pb = avio_alloc_context(_aviobuffer, _buffer_len, 0, (void*)this, cbRead, NULL, NULL);

	//analyzeduration probesize
	/* Open an input stream and read the header. */
	int ret = 0;
	AVDictionary* options = NULL;
    av_dict_set(&options, "fflags", "nobuffer", 0);
	av_dict_set(&options, "rtsp_transport", "tcp", 0);

	if ((ret = avformat_open_input(&_pFormatCtx, 0, 0, 0)) < 0) {
		dzlog_info("Could not open input memory. errno = %x, ret = %d\n", errno, ret);
		return -1;
	}
	av_dict_free(&options);

	if (_bVideo) {
		if (avformat_find_stream_info(_pFormatCtx, 0) < 0) {
			dzlog_info("Failed to retrieve input stream information\n");
			return -1;
		}

		if (fabs(pr._vfps - 0.0f) > FLT_EPSILON) {
			auto s = _pFormatCtx;
			int video_index = 0;
			s->streams[video_index]->avg_frame_rate.den = 1000;
			s->streams[video_index]->avg_frame_rate.num = pr._vfps * 1000;
			s->streams[video_index]->r_frame_rate.den = 1000;
			s->streams[video_index]->r_frame_rate.num = pr._vfps * 1000;
		}
	}
	else {
		if (avformat_find_stream_info(_pFormatCtx, 0) < 0) {
			dzlog_info("Failed to retrieve input stream information\n");
			return -1;
		}
	}

	_pBuff->setRemoveReaded(1);

	return 0;
}