EasyPlayerPro(Windows)流媒体播放器开发之框架讲解

EasyPlayerPro for Windows是基于ffmpeg进行开发的全功能播放器，开发过程中参考了很多开源的播放器，诸如vlc和ffplay等，其中最强大的莫过于vlc，但是鉴于vlc框架过于庞大而其中仍存在诸多问题而舍弃了，而其他的更倾向于演示demo，只能提供部分借鉴意义；故而，EasyPlayerPro 一贯秉承Easy系列小而精，接口简单功能强大的宗旨从新设计了一套框架，该套框架能适应多线程调用以及多个播放实例同时运行，和EasyPlayer一样Easy; 当然，在此也郑重的感谢各大开源播放器以及ffmpeg的作者的无私奉献。

EasyPlayerPro分为三大模块：打开模块，读取流数据模块，解码模块和渲染模块，其中：

(1) 打开模块
打开流模块很简单，教科书式的调用方法：

    player->avformat_context = avformat_alloc_context();    player->avformat_context->interrupt_callback.callback = interrupt_cb;    player->avformat_context->interrupt_callback.opaque = player;    // open input file    AVDictionary *options = NULL;    //av_dict_set(&options, "rtsp_transport", "udp", 0);    if (avformat_open_input(&player->avformat_context, url, fmt, &options) != 0)     {        goto error_handler;    }    // find stream info    if (avformat_find_stream_info(player->avformat_context, NULL) < 0)     {        goto error_handler;    }    // set current audio & video stream    for (i=0,idx=-1,cur=-1; i<(int)player->avformat_context->nb_streams; i++) {switch (type) {    case AVMEDIA_TYPE_AUDIO:        // get last codec context        if (player->acodec_context) {            lastctxt = player->acodec_context;        }        // get new acodec_context & astream_timebase        player->acodec_context   = player->avformat_context->streams[idx]->codec;        player->astream_timebase = player->avformat_context->streams[idx]->time_base;        // reopen codec        if (lastctxt) avcodec_close(lastctxt);        decoder = avcodec_find_decoder(player->acodec_context->codec_id);        if (decoder && avcodec_open2(player->acodec_context, decoder, NULL) == 0) {            player->astream_index = idx;        }        else {            av_log(NULL, AV_LOG_WARNING, "failed to find or open decoder for audio !\n");            player->astream_index = -1;        }        break;    case AVMEDIA_TYPE_VIDEO:        // get last codec context        if (player->vcodec_context) {            lastctxt = player->vcodec_context;        }        // get new vcodec_context & vstream_timebase        player->vcodec_context   = player->avformat_context->streams[idx]->codec;        player->vstream_timebase = player->avformat_context->streams[idx]->time_base;        // reopen codec        if (lastctxt) avcodec_close(lastctxt);        decoder = avcodec_find_decoder(player->vcodec_context->codec_id);        if (decoder && avcodec_open2(player->vcodec_context, decoder, NULL) == 0) {            player->vstream_index = idx;        }        else {            av_log(NULL, AV_LOG_WARNING, "failed to find or open decoder for video !\n");            player->vstream_index = -1;        }        break;    case AVMEDIA_TYPE_SUBTITLE:        return -1; // todo...        }    }    if (idx == -1) return -1;    // for audio    if (player->astream_index != -1)    {        arate   = player->acodec_context->sample_rate;        aformat = player->acodec_context->sample_fmt;        alayout = player->acodec_context->channel_layout;        //++ fix audio channel layout issue        if (alayout == 0) {            alayout = av_get_default_channel_layout(player->acodec_context->channels);        }        //-- fix audio channel layout issue    }    // for video    if (player->vstream_index != -1) {        vrate = player->avformat_context->streams[player->vstream_index]->r_frame_rate;        if (vrate.num / vrate.den >= 100) {            vrate.num = 25;            vrate.den = 1;        }        player->vcodec_context->pix_fmt = vformat;        width   = player->vcodec_context->width;        height  = player->vcodec_context->height;    }

首先，avformat_open_input打开一个流，为了避免在打开流的时候出现阻塞，我们创建一个线程来执行，同时，为了防止ffmpeg内部出现持久行的阻塞，我们传入阻塞回调函数，在关闭流或者其他必要的时候解除阻塞；avformat_find_stream_info获取流的解码信息，根据音视频以及字幕的解码信息初始化解码器；

(2) 读取流数据模块

        retv = av_read_frame(player->avformat_context, packet);        //++ play completed ++//        if (retv < 0)        {            if (player->avformat_context->pb && player->avformat_context->pb->error)            {                       //告知播放实时流中断                player->error_flag = 1;                //创建断线重连错误检测线程                //  [9/4/2017 swordtwelve]                break;            }            player->player_status |= PS_D_PAUSE;            pktqueue_write_post_i(player->pktqueue, packet);            usleep(20*1000);             continue;        }        //-- play completed --//        player->error_flag = 0;//-1=初始化 0=正常 1-n错误代码        // audio        if (packet->stream_index == player->astream_index)        {            pktqueue_write_post_a(player->pktqueue, packet);        }        // video        if (packet->stream_index == player->vstream_index)        {            pktqueue_write_post_v(player->pktqueue, packet);        }        if (  packet->stream_index != player->astream_index            && packet->stream_index != player->vstream_index )        {            av_packet_unref(packet); // free packet            pktqueue_write_post_i(player->pktqueue, packet);        }    }

读取数据模块超级简单，创建一个线程循环执行av_read_frame，读取到一帧就将其放入队列，这里采用了ffplay的阻塞的方式来处理队列的消费者和生产者的问题，这块有待优化，后续将改成无锁循环队列模式，如EasyPlayer。

(3) 解码模块
解码模块分为音频和视频解码模块，音视频的解码流程非常相似，
主要分为三步：
a. 从队列中读取音视频编码数据；
b. 音视频分别采用avcodec_decode_audio4和avcodec_decode_video2进行解码；
c. 音视频渲染；
这里着重讲解视频的解码后的过程，其中涉及到解码后的原始图像数据进行处理，解码出一帧图像以后，我们需要对其进行字幕和图像或者其他的视频图像的叠加，借助ffmpeg强大的图像转换和缩放能力，借助VFX库我们很容易实现：

            consumed = avcodec_decode_video2(player->vcodec_context, vframe, &gotvideo, packet);            if (consumed < 0) {                av_log(NULL, AV_LOG_WARNING, "an error occurred during decoding video.\n");                break;            }            if (gotvideo)             {                // 解码视频帧添加特技处理 [9/7/2017 dingshuai]                // 1. 叠加图片                // 2. 叠加字母                // 3. 画框...                // 对解码帧进行特技处理（字符，图片叠加，添加特效） [Dingshuai 2017/08/07]#if 1                WaterMarkInfo g_waterMarkInfo = player->vfxConfigInfo.warkMarkInfo;                if (g_waterMarkInfo.bIsUseWaterMark)                {                    if (player->vcodec_context->width != vframe->width   ||                         player->vcodec_context->height != vframe->height ||                         player->vfxConfigInfo.warkMarkInfo.bResetWaterMark )                    {                        //初始化水印叠加                        //;表示台标位置：1 == 左上 2 == 右上 3 == 左下 4 == 右下                        //eWaterMarkPos = 3                        //;水印顶点x轴坐标，建议不小于0；不大于视频宽度                        //nLeftTopX = 0                        //;水印顶点y轴坐标，建议不小于0；不大于视频高度                        //nLeftTopY = 480                        //;水印风格：0 - 6                        //eWatermarkStyle = 3                        //;水印图像文件路径LOGO.png                        //strWMFilePath = .\Res\logo.png                        switch (g_waterMarkInfo.eWaterMarkPos)                        {                        case POS_LEFT_TOP:                            g_waterMarkInfo.nLeftTopX = 0;                            g_waterMarkInfo.nLeftTopY = 0;                            break;                        case POS_RIGHT_TOP:                            g_waterMarkInfo.nLeftTopX = vframe->width;                            g_waterMarkInfo.nLeftTopY = 0;                            break;                        case POS_LEFT_BOTTOM:                            g_waterMarkInfo.nLeftTopX = 0;                            g_waterMarkInfo.nLeftTopY = vframe->height;                            break;                        case POS_RIGHT_BOTTOM:                            g_waterMarkInfo.nLeftTopX = vframe->width;                            g_waterMarkInfo.nLeftTopY = vframe->height;                            break;                        }                        player->vfxHandle->SetVideoInVideoParam( 101, 0, 0, vframe->width,                            vframe->height, 100, 100, 100);                        player->vfxHandle->SetLogoImage(g_waterMarkInfo.strWMFilePath, g_waterMarkInfo.nLeftTopX,                            g_waterMarkInfo.nLeftTopY, g_waterMarkInfo.bIsUseWaterMark, g_waterMarkInfo.eWatermarkStyle);                        player->vfxConfigInfo.warkMarkInfo.bResetWaterMark = FALSE;                    }                }                //初始化字幕信息                VideoTittleInfo tittleInfo = player->vfxConfigInfo.tittleInfo;                if(tittleInfo.bResetTittleInfo)                {                    //  -->1、初始化创建字幕指针,并初始化视频长宽参数       m_pVideoVfxMakerInfo->nDesWidth, m_pVideoVfxMakerInfo->nDesHeight,  m_pVideoVfxMakerInfo->strDesBytesType);                    player->vfxHandle->CreateOverlayTitle(vframe->width, vframe->height, ("YUY2"));                    //  -->2、设置字幕文字信息                    LOGFONTA inFont;                    inFont.lfHeight      = tittleInfo.nTittleHeight;                    inFont.lfWidth       = tittleInfo.nTittleWidth;                    inFont.lfEscapement  = 0;                    inFont.lfOrientation = 0;                    inFont.lfWeight      = tittleInfo.nFontWeight;//FW_NORMAL;                    inFont.lfItalic      = 0;                    inFont.lfUnderline   = 0;                    inFont.lfStrikeOut   = 0;                    inFont.lfCharSet        =GB2312_CHARSET;// ANSI_CHARSET;//134                    inFont.lfOutPrecision   =3;// OUT_DEFAULT_PRECIS;                    inFont.lfClipPrecision  = 2;//CLIP_DEFAULT_PRECIS;                    inFont.lfQuality        = 1;//PROOF_QUALITY;                    inFont.lfPitchAndFamily = 0;//49;//49                    strcpy(inFont.lfFaceName, tittleInfo.strFontType);//"华文新魏");//"华文隶书");"隶书"                    POINT pointTitle;                    if(tittleInfo.nMoveType==0)                    {                        pointTitle= tittleInfo.ptStartPosition;                        if(pointTitle.x<=0) pointTitle.x=1;                        if(pointTitle.x>=vframe->width) pointTitle.x=vframe->width/2;                    }                    else if(tittleInfo.nMoveType==1)//从左往右                    {                        pointTitle.x =  -1;                        pointTitle.y = tittleInfo.ptStartPosition.y;                    }                    else if(tittleInfo.nMoveType==2)                    {                        pointTitle.x =  vframe->width+1;                        pointTitle.y = tittleInfo.ptStartPosition.y;                    }                    player->vfxHandle->SetOverlayTitleInfo(tittleInfo.strTittleContent,                         inFont, tittleInfo.nColorR, tittleInfo.nColorG,                        tittleInfo.nColorB, pointTitle);                    //-->3、设置字幕运行抓状态                    player->vfxHandle->SetOverlayTitleState(tittleInfo.nState);                    player->vfxConfigInfo.tittleInfo.bResetTittleInfo = FALSE;                }                if (player->vfxHandle && (g_waterMarkInfo.bIsUseWaterMark || tittleInfo.nState))//logo-水印 + 字幕 + ？？？                {                    if (player->vcodec_context->width != vframe->width   ||                         player->vcodec_context->height != vframe->height )                    {                        if (pVfxBuffer)                        {                            free(pVfxBuffer);                            pVfxBuffer = NULL;                        }                    }                    int nBufSize = vframe->width*vframe->height << 1;                    if (!pVfxBuffer)                    {                        pVfxBuffer = (BYTE*)malloc(nBufSize); //缓存写入源数据                         memset(pVfxBuffer, 0x00, nBufSize);                    }                    AVFrame src;                    av_image_fill_arrays(src.data, src.linesize, pVfxBuffer, outPixelFormat, vframe->width, vframe->height, 1);                    //YUV420 -> YUY2                    ConvertColorSpace(&src, outPixelFormat, vframe, inPixelFormat, vframe->width, vframe->height);//                  av_image_copy_to_buffer(pVfxBuffer, nBufSize,//                      vframe->data, vframe->linesize, AV_PIX_FMT_YUYV422,  vframe->width, vframe->height, 1);                    //水印叠加                    if(g_waterMarkInfo.bIsUseWaterMark)                        player->vfxHandle->AddWaterMask(pVfxBuffer);                    //OSD叠加                    if(tittleInfo.nState)                        player->vfxHandle->DoOverlayTitle(pVfxBuffer);                    //YUY2 -> I420                    //ConvertColorSpace(vframe, inPixelFormat, &src, outPixelFormat, vframe->width, vframe->height);                    av_image_fill_arrays(vframe->data, vframe->linesize, pVfxBuffer, outPixelFormat, vframe->width, vframe->height, 1);                    int nPixelFmt = AV_PIX_FMT_YUYV422;                    player_setparam(player, PARAM_RENDER_OUTFORMAT, &nPixelFmt);                 }                else                {                    int nPixelFmt = AV_PIX_FMT_YUV420P;                    player_setparam(player, PARAM_RENDER_OUTFORMAT, &nPixelFmt);                 }#endif

由于视频渲染需要一定的时间，我们也将解码帧数据进入队列进行缓存，从而保证播放的流畅性；

(4) 渲染模块
渲染模块分为音频渲染和视频渲染，音频渲染即播放，使用waveOutOpen，waveOutWrite等waveout函数即可实现，下面重点说一下视频渲染，视频渲染通俗讲也就是图像绘制，Windows平台可采用D3D,DDraw, GDI，OpenGL等多种方式进行呈现，本文主要采用3种渲染方式，D3D，GDI和OpenGL；
为了保证渲染的流畅性，我们创建线程执行渲染，
a. 读取解码图像队列；
b. 音视频时间戳同步处理；
c. D3D/gdi/openGL渲染：

关于EasyPlayerPro

EasyPlayerPro是一款全功能的流媒体播放器，支持RTSP、RTMP、HTTP、HLS、UDP、RTP等多种流媒体协议播放、支持本地文件播放，支持本地抓拍、本地录像、播放旋转、多屏播放等多种功能特性，稳定、高效、可靠，支持Windows、Android、iOS三个平台，目前在多家教育、安防、行业型公司，都得到的应用，广受好评！

EasyPlayerPro：https://github.com/EasyDSS/EasyPlayerPro

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