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 fileAVDictionary *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 infoif (avformat_find_stream_info(player->avformat_context, NULL) < 0) {goto error_handler;}// set current audio & video streamfor (i=0,idx=-1,cur=-1; i<(int)player->avformat_context->nb_streams; i++) {
switch (type) {case AVMEDIA_TYPE_AUDIO:// get last codec contextif (player->acodec_context) {lastctxt = player->acodec_context;}// get new acodec_context & astream_timebaseplayer->acodec_context   = player->avformat_context->streams[idx]->codec;player->astream_timebase = player->avformat_context->streams[idx]->time_base;// reopen codecif (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 contextif (player->vcodec_context) {lastctxt = player->vcodec_context;}// get new vcodec_context & vstream_timebaseplayer->vcodec_context   = player->avformat_context->streams[idx]->codec;player->vstream_timebase = player->avformat_context->streams[idx]->time_base;// reopen codecif (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 audioif (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 issueif (alayout == 0) {alayout = av_get_default_channel_layout(player->acodec_context->channels);}//-- fix audio channel layout issue}// for videoif (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// audioif (packet->stream_index == player->astream_index){pktqueue_write_post_a(player->pktqueue, packet);}// videoif (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 packetpktqueue_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 1WaterMarkInfo 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.pngswitch (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;//134inFont.lfOutPrecision   =3;// OUT_DEFAULT_PRECIS;inFont.lfClipPrecision  = 2;//CLIP_DEFAULT_PRECIS;inFont.lfQuality        = 1;//PROOF_QUALITY;inFont.lfPitchAndFamily = 0;//49;//49strcpy(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 -> YUY2ConvertColorSpace(&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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