1.xdemux
图片来源：https://jiedi.ke.qq.com/

int main(int argc, char *argv[])
{xdemux demux;const char* path = "E:\\ffmpeg\\test.flv";const char* url = "rtmp://192.168.1.10/live?vhost=ossrs.net/livestream'<br>url6 = ";//url = "v1080.mp4";cout << "demux.Open = " << demux.Open(path)<<endl;cout << "CopyVPara = " << demux.CopyVPara( ) << endl;cout << "CopyAPara = " << demux.CopyAPara() << endl;for (;;){AVPacket* pkt = demux.read();if (!pkt)break;}QApplication a(argc, argv);Xplay2 w;w.show();return a.exec();
}

xdemux.h

#pragma once
#include <mutex>
struct AVFormatContext;
struct AVPacket;
struct AVCodecParameters;
class xdemux
{
public://打开媒体文件，或者流媒体 rtmp http rstpvirtual bool Open(const char* url);xdemux();virtual ~xdemux();virtual AVPacket* read();//媒体总时长（毫秒）int totalMs = 0;
protected:std::mutex mux;//解封装上下文AVFormatContext* ic = NULL;//音视频索引，读取时区分音视频int videoStream = 0;int audioStream = 1;
};

xdemux.cpp

#include "XDemux.h"
#include <iostream>
#include<mutex>
extern "C" {
#include "libavformat/avformat.h"
}
#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avutil.lib")
#pragma comment(lib,"avcodec.lib")
using namespace std;
static double r2d(AVRational r)
{return r.den == 0 ? 0 : (double)r.num / (double)r.den;
}
xdemux::xdemux()
{static bool isFirst = true;mutex mux;mux.lock();if (isFirst){//初始化封装库  被弃用了//av_register_all();//初始化网络库 （可以打开rtsp rtmp http 协议的流媒体视频）avformat_network_init();isFirst = false;}mux.unlock();
}
xdemux:: ~xdemux()
{
}

通过实例化xdemux的对象调用xdemux的构造函数，在这里面会进行网络库等初始化

bool xdemux::Open(const char* url)
{//参数设置AVDictionary* opts = NULL;//设置rtsp流已tcp协议打开av_dict_set(&opts, "rtsp_transport", "tcp", 0);//网络延时时间av_dict_set(&opts, "max_delay", "500", 0);mux.lock();int re = avformat_open_input(&ic,url,0,  // 0表示自动选择解封器&opts //参数设置，比如rtsp的延时时间);if (re != 0){mux.unlock();char buf[1024] = { 0 };av_strerror(re, buf, sizeof(buf) - 1);cout << "open " << url << " failed! :" << buf << endl;return false;}cout << "open " << url << " success! " << endl;//获取流信息 re = avformat_find_stream_info(ic, 0);//总时长 毫秒int totalMs = ic->duration / (AV_TIME_BASE / 1000);cout << "totalMs = " << totalMs << endl;//打印视频流详细信息av_dump_format(ic, 0, url, 0);//获取视频流videoStream = av_find_best_stream(ic, AVMEDIA_TYPE_VIDEO, -1, -1, NULL, 0);AVStream* as = ic->streams[videoStream];cout << "=======================================================" << endl;cout << videoStream << "视频信息" << endl;cout << "codec_id = " << as->codecpar->codec_id << endl;cout << "format = " << as->codecpar->format << endl;cout << "width=" << as->codecpar->width << endl;cout << "height=" << as->codecpar->height << endl;//帧率 fps 分数转换cout << "video fps = " << r2d(as->avg_frame_rate) << endl;cout << "=======================================================" << endl;cout << audioStream << "音频信息" << endl;//获取音频流audioStream = av_find_best_stream(ic, AVMEDIA_TYPE_AUDIO, -1, -1, NULL, 0);as = ic->streams[audioStream];cout << "codec_id = " << as->codecpar->codec_id << endl;cout << "format = " << as->codecpar->format << endl;cout << "sample_rate = " << as->codecpar->sample_rate << endl;cout << "channels = " << as->codecpar->channels << endl;cout << "frame_size = " << as->codecpar->frame_size << endl;//1024 * 2 * 2 = 4096 fps =sample_rate/frame_sizemux.unlock();return true;
}

2.xdemux:: read()

然后通过xdemux的open方法去解封装，在这个函数中将解封装后的信息放到ic中
解封装后要去读每一个packet：AVPacket* pkt = demux.read();

AVPacket*  xdemux:: read()
{mux.lock();if (!ic)//打开的话ic是0，否则是1//做容错，虽然在main函数中看起来是read在初始化之后被调用，但假如初始化很慢，会多进程调用read，这时候ic就是空的{mux.unlock();return 0;}

读和打开不能同时进行，ic在读时初始化，若读一半ic变了的话会发生错误
if (!ic)//打开的话ic是0，否则是1
做容错，虽然在main函数中看起来是read在初始化之后被调用，但假如初始化很慢，会多进程调用read，这时候ic就是空的

	AVPacket* pkt=av_packet_alloc();//只是对象空间，并没有分配数据空间int re=av_read_frame(ic, pkt);//分配数据空间if (re!=0)//打开的话re是0，否则为负{mux.unlock();av_packet_free(&pkt);return 0;}//为了后面做同步，pts转换为毫秒pkt->pts = pkt->pts * (1000 * (r2d(ic->streams[pkt->stream_index]->time_base)));pkt->dts = pkt->dts * (1000 * (r2d(ic->streams[pkt->stream_index]->time_base)));mux.unlock();cout << " " << pkt->dts  << flush;return pkt;
}

将解封装后的信息以ic做为桥梁传进int re=av_read_frame(ic, pkt);将读出的信息放在AVPacket中并用pkt指向（标记）出这块空间，读完一帧会自动读下一帧

下面显示的是dts(解码时间戳），因为是通过packet打印的，每个packet里有很多帧的信息，所有每个时间戳之间存在一定的间隔

3.avcodecparameters

解封装获得的信息需要传给decode（）

结构体AVCodecParameters中有个指针uint8_t *extradata，
*Extra binary data needed for initializing the decoder, codec - dependent.
*Must be allocated with av_malloc() and will be freed by
avcodec_parameters_free().
//结构体中其他成员可以直接复制，但当结构体释放的时候指针指向的成员也会被释放，直接复制为浅拷贝，就会宕掉
//动态链接库中申请和释放

AVCodecParameters* xdemux::CopyVPara()
{mux.lock();//用ic了if (!ic)//可能没打开{mux.unlock();return NULL;}AVCodecParameters* pa = avcodec_parameters_alloc();avcodec_parameters_copy(ic->streams[videoStream]->codecpar, pa);mux.unlock();return pa;
}
AVCodecParameters* xdemux::CopyAPara()
{mux.lock();if (!ic)//可能没打开{mux.unlock();return NULL;}AVCodecParameters* pa = avcodec_parameters_alloc();avcodec_parameters_copy(ic->streams[audioStream]->codecpar, pa);return pa;
}

复制视频和音频信息
先做容错判断，
再开辟空间
再调用复制函数，将ic中的信息放到pa中

主函数调用方法：
cout << "CopyVPara = " << demux.CopyVPara( ) << endl;
cout << "CopyAPara = " << demux.CopyAPara() << endl;

打印了pa的地址