FFmpeg拉取rtmp流转udp输出播放

     用ffmpeg可以拉取rtmp流，比如湖南卫视的：rtmp://58.200.131.2:1935/livetv/hunantv

     在vlc播放器可以测试看看，网速不好的，会有延时, 媒体----打开网络串流，填入湖南卫视的rtmp地址。

        播放如下

        太卡了，没专业播放器爽。

       下面开始本篇的主题，拉取rtmp流，用udp转发出去，至于怎么处理就看软件功能需求了。ffmpeg环境自己配吧，也不是很难，api 不会的可以看英文注释，代码如下：

#include "stdafx.h"
#include "pch.h"
#include 
#include 
#include 
#include 
using namespace std;

AVFormatContext *inputContext = nullptr;
AVFormatContext * outputContext;
int64_t lastReadPacktTime ;

static int interrupt_cb(void *ctx)
{
	int  timeout  = 10;  //比如拉取湖南卫视的rtmp流，可能延时比较长
  	if(av_gettime() - lastReadPacktTime > timeout *1000 *1000)
	{
		return -1;
	}
	return 0;
}

int OpenInput(string inputUrl)
{
	inputContext = avformat_alloc_context();	
	lastReadPacktTime = av_gettime();
	inputContext->interrupt_callback.callback = interrupt_cb;
	int ret = avformat_open_input(&inputContext, inputUrl.c_str(), nullptr,nullptr);
	if(ret < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "Input file open input failed\n");
		return  ret;
	}
	ret = avformat_find_stream_info(inputContext,nullptr);
	if(ret < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "Find input file stream inform failed\n");
	}
	else
	{
		av_log(NULL, AV_LOG_FATAL, "Open input file  %s success\n",inputUrl.c_str());
	}
	return ret;
}

shared_ptr ReadPacketFromSource()
{
	shared_ptr packet(static_cast(av_malloc(sizeof(AVPacket))), [&](AVPacket *p) { av_packet_free(&p); av_freep(&p);});
	av_init_packet(packet.get());
	lastReadPacktTime = av_gettime();
	int ret = av_read_frame(inputContext, packet.get());
	if(ret >= 0)
	{
		return packet;
	}
	else
	{
		return nullptr;
	}
}

void av_packet_rescale_ts(AVPacket *pkt, AVRational src_tb, AVRational dst_tb)
{
	if (pkt->pts != AV_NOPTS_VALUE)
		pkt->pts = av_rescale_q(pkt->pts, src_tb, dst_tb);
	if (pkt->dts != AV_NOPTS_VALUE)
		pkt->dts = av_rescale_q(pkt->dts, src_tb, dst_tb);
	if (pkt->duration > 0)
		pkt->duration = av_rescale_q(pkt->duration, src_tb, dst_tb);
}

int WritePacket(shared_ptr packet)
{
	auto inputStream = inputContext->streams[packet->stream_index];
	auto outputStream = outputContext->streams[packet->stream_index];				
	av_packet_rescale_ts(packet.get(),inputStream->time_base,outputStream->time_base);
	return av_interleaved_write_frame(outputContext, packet.get());
}

int OpenOutput(string outUrl)
{
	int ret  = avformat_alloc_output_context2(&outputContext, nullptr, "mpegts", outUrl.c_str());
	if(ret < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "open output context failed\n");
		goto Error;
	}

	ret = avio_open2(&outputContext->pb, outUrl.c_str(), AVIO_FLAG_WRITE,nullptr, nullptr);	
	if(ret < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "open avio failed");
		goto Error;
	}

	for(int i = 0; i < inputContext->nb_streams; i++)
	{
		AVStream * stream = avformat_new_stream(outputContext, inputContext->streams[i]->codec->codec);				
		ret = avcodec_copy_context(stream->codec, inputContext->streams[i]->codec);	
		if(ret < 0)
		{
			av_log(NULL, AV_LOG_ERROR, "copy coddec context failed");
			goto Error;
		}
	}

	ret = avformat_write_header(outputContext, nullptr);
	if(ret < 0)
	{
		av_log(NULL, AV_LOG_ERROR, "format write header failed");
		goto Error;
	}

	av_log(NULL, AV_LOG_FATAL, " Open output file success %s\n",outUrl.c_str());			
	return ret ;
Error:
	if(outputContext)
	{
		for(int i = 0; i < outputContext->nb_streams; i++)
		{
			avcodec_close(outputContext->streams[i]->codec);
		}
		avformat_close_input(&outputContext);
	}
	return ret ;
}

void CloseInput()
{
	if(inputContext != nullptr)
	{
		avformat_close_input(&inputContext);
	}
}

void CloseOutput()
{
	if(outputContext != nullptr)
	{
		for(int i = 0 ; i < outputContext->nb_streams; i++)
		{
			AVCodecContext *codecContext = outputContext->streams[i]->codec;
			avcodec_close(codecContext);
		}
		avformat_close_input(&outputContext);
	}
}

void Init()
{
	av_register_all();
	avfilter_register_all();
	avformat_network_init();
	av_log_set_level(AV_LOG_ERROR);
}

int _tmain(int argc, _TCHAR* argv[])
{
	Init();
	int ret = OpenInput("rtmp://58.200.131.2:1935/livetv/hunantv");
	if(ret >= 0)
	{
		ret = OpenOutput("udp://127.0.0.1:6789"); 
	}

	if(ret <0) 
		goto Error;

	while(true)
	{
		auto packet = ReadPacketFromSource();
		if(packet)
		{
			ret = WritePacket(packet);
			if(ret >= 0)
			{
				cout<<"WritePacket Success!"<

      需要注意的是，由于拉取时网络情况会有影响，那么延时设置需要长点，我设为了10秒，如下所示

static int interrupt_cb(void *ctx)
{
	int  timeout  = 10;  //比如拉取湖南卫视的rtmp流，可能延时比较长
  	if(av_gettime() - lastReadPacktTime > timeout *1000 *1000)
	{
		return -1;
	}
	return 0;
}

        编译测试，用ffplay可以播放，由于电脑，网速等原因，可能会有一定的卡顿，比如先出声音，画面延迟一会儿才出现。如下：

        以上有不当之处请指出，或在评论区留言。