ffmpeg解码h264流数据并用opencv显示

    最近做的一个项目，需要播放服务端传过来的h264裸流数据，于是做了一个简易的播放器，采用ffmpeg解码h264并用opencv显示图像。实现原理很简单，首先接收到一个完整的h264帧之后传给ffmpeg的AVPacket，然后调用avcodec_send_packet()和avcodec_receive_frame()解码，得到一个AVFrame，然后调用sws_scale()把解码后的yuv图像转换成opencv能使用的RGB图像，然后每解码转换一帧数据就调用一次cv::imshow()显示图像，具体实现代码如下：

//H264ToCVShow.h
#ifndef _H264TOCVSHOW_H
#define _H264TOCVSHOW_H

//#define __STDC_CONSTANT_MACROS
#include <stdio.h>
// Opencv
extern "C" {
#include "libavutil/avutil.h"
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavutil/imgutils.h"
};
#include <opencv2/opencv.hpp>
#include <opencv2/core.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/imgproc.hpp>
#include <opencv2/objdetect.hpp>

#include <thread>
#include <string>

class H264ToCVShow {

public :

    H264ToCVShow(std::string winName);
    ~H264ToCVShow(); 
    void init();
    void decode(unsigned char *inputbuf, size_t size);
    void start();
    void play();
    cv::Mat getMat();

private:
    
    const AVCodec *codec;
    AVCodecContext *c = nullptr;
    int frame_count;
    AVFrame *frame;
    AVPacket avpkt;
    struct SwsContext *img_convert_ctx;
    cv::Mat pCvMat;
    bool matReady;
    std::thread *play_th = nullptr;
    std::string windowName;
};

#endif 

//H264ToCVShow.cpp
#include "H264ToCVShow.h"
#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avutil.lib")
#pragma comment(lib,"avcodec.lib")
#pragma comment(lib,"swscale.lib")
#pragma comment(lib,"opencv_world320d.lib")


void H264ToCVShow::init() {

    matReady = false;
    av_init_packet(&avpkt);

    codec = avcodec_find_decoder(AV_CODEC_ID_H264);
    if (!codec) {
        fprintf(stderr, "Codec not found\n");
        exit(1);
    }
    c = avcodec_alloc_context3(codec);
    if (!c) {
        fprintf(stderr, "Could not allocate video codec context\n");
        exit(1);
    }

    if (avcodec_open2(c, codec, NULL) < 0) {
        fprintf(stderr, "Could not open codec\n");
        exit(1);
    }

    frame = av_frame_alloc();
    if (!frame) {
        fprintf(stderr, "Could not allocate video frame\n");
        exit(1);
    }

    frame_count = 0;

}


void H264ToCVShow::decode(unsigned char *inputbuf, size_t size){

    avpkt.size = size;
    if(avpkt.size == 0)
        return;

    avpkt.data = inputbuf;
	int ret = avcodec_send_packet(c, &avpkt);
	if (ret != 0)
	{
		printf("avcodec_send_packet error\n");
	}
	ret = avcodec_receive_frame(c, frame);
	while (true)
	{
		if (ret == 0)
		{
			int width = frame->width;
			int height = frame->height;

			// Allocate the opencv mat and store its stride in a 1-element array
			if (pCvMat.rows != height || pCvMat.cols != width || pCvMat.type() != CV_8UC3) pCvMat = cv::Mat(height, width, CV_8UC3);
			int cvLinesizes[1];
			cvLinesizes[0] = pCvMat.step1();

			// Convert the colour format and write directly to the opencv matrix
			SwsContext* conversion = sws_getContext(width, height, (AVPixelFormat)frame->format, width, height, AVPixelFormat::AV_PIX_FMT_BGR24, SWS_FAST_BILINEAR, NULL, NULL, NULL);
			sws_scale(conversion, frame->data, frame->linesize, 0, height, &pCvMat.data, cvLinesizes);
			sws_freeContext(conversion);
			matReady = true;
			ret = avcodec_receive_frame(c, frame);
			if (ret != 0) {
				matReady = false;
				break;
			}
		}
		else {
			matReady = false;
			break;
		}
	}
}

void H264ToCVShow::play() {
    while(true)
    {
        if(matReady){   
            cv::imshow(windowName,pCvMat);
            cv::waitKey(1);
        }
    }
}

void H264ToCVShow::start()
{
    play_th = new std::thread(&H264ToCVShow::play,this);
    //play_th->join();
}

H264ToCVShow::H264ToCVShow(std::string winName) {
    this->windowName = winName;
    init();
}
H264ToCVShow::~H264ToCVShow() {
    play_th->join();
    delete play_th;
    play_th = nullptr;
}
cv::Mat H264ToCVShow::getMat() {
    if(matReady){
        return pCvMat;
    }
    else{
        return cv::Mat();
    }
}