VC++实现视频聊天：FFmpeg解码+SDL播放视频

经过网络传输接收到的码流，已经存放在公共链表 PacketNode_t 中，码流经过解码成YUV或RGB后才能播放，接下来就介绍FFmpeg解码过程和 SDL 播放视频。

FFmpeg 解码

码流解码很消耗CPU资源，所以要单独开解码线程，在这之前应该进行解码器的初始化。

解码器初始化

AVFrame *m_picture;
AVFrame *m_pFrameYUV;
AVCodec *m_codec;
AVCodecContext *m_pCodecCtx;
struct SwsContext *m_pImgCtx;
AVCodecParserContext *m_pCodecParserCtx;
AVFormatContext *m_pFmtCtx;
int      m_PicBytes;
uint8_t* m_PicBuf;

BOOL CVideoDlg::InitDecoder()
{

    int Ret = 0;
    av_register_all();        //注册所有解码器
    m_pFmtCtx = avformat_alloc_context(); 
    if (NULL == m_pFmtCtx)
    {
        Printf("avformat_alloc_context failed!\n");
    }

    //寻找解码器
    m_codec = avcodec_find_decoder(CODEC_ID_H265);
    if (!m_codec)
    {
        Printf(TRUE,FALSE,"Codec not found !\n");
        return 0;
    }
    //解码器结构
    m_pCodecCtx = avcodec_alloc_context3(m_codec);
    m_pCodecParserCtx = av_parser_init(AV_CODEC_ID_H264);
    if (!m_pCodecParserCtx){
        Printf(TRUE,FALSE,"Could not allocate video parser context\n");
        return 0;
    }

    //打开解码器
    Ret = avcodec_open2(m_pCodecCtx, m_codec, NULL);
    if (Ret < 0)
    {
        Printf(TRUE,FALSE,"Could not open codec !\n");
        return 0;
    }

    //AVFrame分配空间
    m_picture = av_frame_alloc();
    m_pFrameYUV = av_frame_alloc();

    m_PicBytes = 0;
    m_PicBuf = NULL;
    m_pImgCtx = NULL;

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER)) {
        AfxMessageBox(_T("Could not initialize SDL\n"));
        return 0;
    }

    return TRUE;
}

解码线程

在初始化过程中，已经通过定时器 SetTimer() 实现解码线程的声明：

void CVideoDlg::OnTimer(UINT_PTR nIDEvent)
{
    if (0 == thread_exit)
    {
        return;
    }
    if(123 == nIDEvent)
    {
        pThreadPlay = AfxBeginThread(Thread_Play,this); //开启线程
        KillTimer(123);
    }
}

Thread_Play就是解码线程函数的地址，接下来去实现这个函数：

static UINT Thread_Play(VOID *pVoid)
{
    CVideoDlg *pDlg = (CVideoDlg*) pVoid;   //指针绑定对话框类
    pDlg->FFmpegPlayer();                  //FFmpeg解码并播放
    return 0;
}

void CVideoDlg::FFmpegPlayer()
{
    int Ret = 0;
    int64_t pos = 0;
    int vid_idx,i;
    AVPacket pkt;
    av_init_packet(&pkt);
    //判断视频
    for( i = 0; i < m_pFmtCtx->nb_streams; i++)
    {
        if(m_pFmtCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
        {
            vid_idx = i;
        }
    }
    //显示在MFC控件上
    screen_w = g_width;
    screen_h = g_height;
    screen = SDL_CreateWindowFrom(GetDlgItem(IDC_SCREEN)->GetSafeHwnd());
    if (!screen) {
        AfxMessageBox(_T("SDL: could not create window - exiting\n"));
        return ;
    }
    sdlRenderer = SDL_CreateRenderer(screen, -1, 0);
    sdlTexture  = SDL_CreateTexture(sdlRenderer, SDL_PIXELFORMAT_IYUV, SDL_TEXTUREACCESS_STREAMING, screen_w, screen_h);

    sdlRect.x = 0;
    sdlRect.y = 0;
    sdlRect.w = screen_w;
    sdlRect.h = screen_h;

    while (1)
    {
        SDL_WaitEvent(&g_event);
        if (g_event.type != SFM_BREAK_EVENT)  /
        {
            if (!packetList.empty())
            {
                //将码流数据复制到AvPacket中
                cs.Lock();
                pkt.size  = packetList.front().length;
                pkt.data  = packetList.front().buf;
                pkt.flags = packetList.front().flags;
                pkt.stream_index = 0;
                pkt.duration = 48000;
                pkt.pos += pos;
                pos = packetList.front().length;
                packetList.pop_front();
                cs.Unlock();    

                //解码码流
                DecodeVideoFrame(&pkt);
            }
            //释放数据包
            av_free_packet(&pkt);
            Sleep(10);
        }
        else
        {
            break;
        }

    }
    Printf("跳出循环，编码结束;\n");
}

解码后播放视频

/*将码流数据解码成视频帧，并进行格式转换，
然后通过SDL播放在MFC对话框上*/
BOOL CVideoDlg::DecodeVideoFrame(AVPacket *pkt)
{

    int Ret = -1;
    int got_picture = 0;
    //将pkt的码流解码到m_picture中
    Ret = avcodec_decode_video2(m_pCodecCtx,m_picture,&got_picture,pkt);
    if (Ret < 0)
    {
        Printf("Error while decoding video frame\n");
        return 0;
    }
    if(1 != got_picture)
    {
        Printf("could not get decoded video frame\n");
        return 0;
    }
    int width  = m_pCodecCtx->width;
    int height = m_pCodecCtx->height;
    //获得像素大小
    m_PicBytes = avpicture_get_size(PIX_FMT_YUV420P,width,height);
    m_PicBuf = new uint8_t[m_PicBytes];

    //为结构体m_pFrame分配存缓冲数据的buffer
    avpicture_fill((AVPicture*)m_pFrameYUV,m_PicBuf,PIX_FMT_YUV420P,width,height);
    if (!m_pImgCtx)
    {
        //将解码后的帧数据转换成YUV420数据
        m_pImgCtx = sws_getContext(width,height,
                    m_pCodecCtx->pix_fmt,width,height,   
                  PIX_FMT_YUV420P,SWS_BICUBIC,NULL,NULL,NULL);
    } 

    //转换数据格式
    sws_scale(m_pImgCtx,(const uint8_t* const*)m_picture->data, m_picture->linesize,0, height, m_pFrameYUV->data, m_pFrameYUV->linesize); 
    //SDL显示------------------------
    SDL_UpdateTexture(sdlTexture, NULL, m_pFrameYUV->data[0], m_pFrameYUV->linesize[0]);
    SDL_RenderClear(sdlRenderer);
    SDL_RenderCopy(sdlRenderer, sdlTexture, NULL, NULL);
    SDL_RenderPresent(sdlRenderer);
    //SDL End-----------------------
    delete[] m_PicBuf; //释放内存
    return Ret;
}

到此，一个视频聊天软件经过：视频采集、编码、码流网络传输、解码、播放流程，终于可以实现了。