=====================================================最简单的基于FFmpeg的AVDevice例子文章列表：
最简单的基于FFmpeg的AVDevice例子（读取摄像头）
最简单的基于FFmpeg的AVDevice例子（屏幕录制）=====================================================
FFmpeg中有一个和多媒体设备交互的类库：Libavdevice。使用这个库可以读取电脑的多媒体设备的数据，或者输出数据到指定的多媒体设备上。
计划写2个有关FFmpeg的libavdevice类库的例子。上篇文章记录了一个基于FFmpeg的Libavdevice类库读取摄像头数据的例子。本篇文章记录一个基于FFmpeg的Libavdevice类库录制屏幕的例子。本文程序录制当前桌面内容并且解码显示出来。有关解码显示方面的代码本文不再详述，可以参考文章：《100行代码实现最简单的基于FFMPEG+SDL的视频播放器（SDL1.x）》
抓屏方法
上篇文章记录了libavdevice的使用方法，本文不再重复。在Windows系统使用libavdevice抓取屏幕数据有两种方法：gdigrab和dshow。下文分别介绍。1.gdigrabgdigrab是FFmpeg专门用于抓取Windows桌面的设备。非常适合用于屏幕录制。它通过不同的输入URL支持两种方式的抓取：（1）“desktop”：抓取整张桌面。或者抓取桌面中的一个特定的区域。（2）“title={窗口名称}”：抓取屏幕中特定的一个窗口（目前中文窗口还有乱码问题）。gdigrab另外还支持一些参数，用于设定抓屏的位置：offset_x：抓屏起始点横坐标。offset_y：抓屏起始点纵坐标。video_size：抓屏的大小。framerate：抓屏的帧率。参考的代码如下：
//Use gdigrab AVDictionary* options = NULL; //Set some options //grabbing frame rate //av_dict_set(&options,"framerate","5",0); //The distance from the left edge of the screen or desktop //av_dict_set(&options,"offset_x","20",0); //The distance from the top edge of the screen or desktop //av_dict_set(&options,"offset_y","40",0); //Video frame size. The default is to capture the full screen //av_dict_set(&options,"video_size","640×480",0); AVInputFormat *ifmt=av_find_input_format("gdigrab"); if(avformat_open_input(&pFormatCtx,"desktop",ifmt,&options)!=0){ printf("Couldn’t open input stream.（无法打开输入流）\n"); return -1; }2.dshow使用dshow抓屏需要安装抓屏软件：screen-capture-recorder软件地址：下载软件安装完成后，可以指定dshow的输入设备为“screen-capture-recorder”即可。有关dshow设备的使用方法在上一篇文章中已经有详细叙述，这里不再重复。参考的代码如下：AVInputFormat *ifmt=av_find_input_format("dshow"); if(avformat_open_input(&pFormatCtx,"video=screen-capture-recorder",ifmt,NULL)!=0){ printf("Couldn’t open input stream.（无法打开输入流）\n"); return -1; }
注：上述两种抓屏方法也可以直接使用ffmpeg.exe的命令行完成，可以参考文章：
FFmpeg获取DirectShow设备数据（摄像头，录屏）
在Linux下可以使用x11grab抓屏，在MacOS下可以使用avfoundation抓屏，在这里不再详细叙述。
代码
下面直接贴上程序代码：
/** * 最简单的基于FFmpeg的AVDevice例子（屏幕录制） * Simplest FFmpeg Device (Screen Capture) * * 雷霄骅 Lei Xiaohua * leixiaohua1020@126.com * 中国传媒大学/数字电视技术 * Communication University of China / Digital TV Technology * * * 本程序实现了屏幕录制功能。可以录制并播放桌面数据。是基于FFmpeg * 的libavdevice类库最简单的例子。通过该例子，可以学习FFmpeg中 * libavdevice类库的使用方法。 * 本程序在Windows下可以使用2种方式录制屏幕： * 1.gdigrab: Win32下的基于GDI的屏幕录制设备。 *抓取桌面的时候，，输入URL为“desktop”。 * 2.dshow: 使用Directshow。注意需要安装额外的软件screen-capture-recorder * 在Linux下可以使用x11grab录制屏幕。 * 在MacOS下可以使用avfoundation录制屏幕。 * * This software capture screen of computer. It’s the simplest example * about usage of FFmpeg’s libavdevice Library. * It’s suiltable for the beginner of FFmpeg. * This software support 2 methods to capture screen in Microsoft Windows: * 1.gdigrab: Win32 GDI-based screen capture device. *Input URL in avformat_open_input() is "desktop". * 2.dshow: Use Directshow. Need to install screen-capture-recorder. * It use x11grab to capture screen in Linux. * It use avfoundation to capture screen in MacOS. */#include <stdio.h>#define __STDC_CONSTANT_MACROS#ifdef _WIN32//Windowsextern "C"{#include "libavcodec/avcodec.h"#include "libavformat/avformat.h"#include "libswscale/swscale.h"#include "libavdevice/avdevice.h"#include "SDL/SDL.h"};#else//Linux…#ifdef __cplusplusextern "C"{#endif#include <libavcodec/avcodec.h>#include <libavformat/avformat.h>#include <libswscale/swscale.h>#include <libavdevice/avdevice.h>#include <SDL/SDL.h>#ifdef __cplusplus};#endif#endif//Output YUV420P #define OUTPUT_YUV420P 0//’1′ Use Dshow //’0′ Use GDIgrab#define USE_DSHOW 0//Refresh Event#define SFM_REFRESH_EVENT (SDL_USEREVENT + 1)int thread_exit=0;int sfp_refresh_thread(void *opaque){while (thread_exit==0) {SDL_Event event;event.type = SFM_REFRESH_EVENT;SDL_PushEvent(&event);SDL_Delay(40);}return 0;}//Show Dshow Devicevoid show_dshow_device(){AVFormatContext *pFormatCtx = avformat_alloc_context();AVDictionary* options = NULL;av_dict_set(&options,"list_devices","true",0);AVInputFormat *iformat = av_find_input_format("dshow");printf("========Device Info=============\n");avformat_open_input(&pFormatCtx,"video=dummy",iformat,&options);printf("================================\n");}//Show AVFoundation Devicevoid show_avfoundation_device(){AVFormatContext *pFormatCtx = avformat_alloc_context();AVDictionary* options = NULL;av_dict_set(&options,"list_devices","true",0);AVInputFormat *iformat = av_find_input_format("avfoundation");printf("==AVFoundation Device Info===\n");avformat_open_input(&pFormatCtx,"",iformat,&options);printf("=============================\n");}int main(int argc, char* argv[]){AVFormatContext*pFormatCtx;inti, videoindex;AVCodecContext*pCodecCtx;AVCodec*pCodec;av_register_all();avformat_network_init();pFormatCtx = avformat_alloc_context();//Open File//char filepath[]="src01_480x272_22.h265";//avformat_open_input(&pFormatCtx,filepath,NULL,NULL)//Register Deviceavdevice_register_all();//Windows#ifdef _WIN32#if USE_DSHOW//Use dshow////Need to Install screen-capture-recorder//screen-capture-recorder//Website: //AVInputFormat *ifmt=av_find_input_format("dshow");if(avformat_open_input(&pFormatCtx,"video=screen-capture-recorder",ifmt,NULL)!=0){printf("Couldn’t open input stream.\n");return -1;}#else//Use gdigrabAVDictionary* options = NULL;//Set some options//grabbing frame rate//av_dict_set(&options,"framerate","5",0);//The distance from the left edge of the screen or desktop//av_dict_set(&options,"offset_x","20",0);//The distance from the top edge of the screen or desktop//av_dict_set(&options,"offset_y","40",0);//Video frame size. The default is to capture the full screen//av_dict_set(&options,"video_size","640×480",0);AVInputFormat *ifmt=av_find_input_format("gdigrab");if(avformat_open_input(&pFormatCtx,"desktop",ifmt,&options)!=0){printf("Couldn’t open input stream.\n");return -1;}#endif#elif defined linux//LinuxAVDictionary* options = NULL;//Set some options//grabbing frame rate//av_dict_set(&options,"framerate","5",0);//Make the grabbed area follow the mouse//av_dict_set(&options,"follow_mouse","centered",0);//Video frame size. The default is to capture the full screen//av_dict_set(&options,"video_size","640×480",0);AVInputFormat *ifmt=av_find_input_format("x11grab");//Grab at position 10,20if(avformat_open_input(&pFormatCtx,":0.0+10,20",ifmt,&options)!=0){printf("Couldn’t open input stream.\n");return -1;}#elseshow_avfoundation_device();//MacAVInputFormat *ifmt=av_find_input_format("avfoundation");//Avfoundation//:if(avformat_open_input(&pFormatCtx,"1",ifmt,NULL)!=0){printf("Couldn’t open input stream.\n");return -1;}#endifif(avformat_find_stream_info(pFormatCtx,NULL)<0){printf("Couldn’t find stream information.\n");return -1;}videoindex=-1;for(i=0; i<pFormatCtx->nb_streams; i++) if(pFormatCtx->streams[i]->codec->codec_type==AVMEDIA_TYPE_VIDEO){videoindex=i;break;}if(videoindex==-1){printf("Didn’t find a video stream.\n");return -1;}pCodecCtx=pFormatCtx->streams[videoindex]->codec;pCodec=avcodec_find_decoder(pCodecCtx->codec_id);if(pCodec==NULL){printf("Codec not found.\n");return -1;}if(avcodec_open2(pCodecCtx, pCodec,NULL)<0){printf("Could not open codec.\n");return -1;}AVFrame*pFrame,*pFrameYUV;pFrame=av_frame_alloc();pFrameYUV=av_frame_alloc();//uint8_t *out_buffer=(uint8_t *)av_malloc(avpicture_get_size(PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));//avpicture_fill((AVPicture *)pFrameYUV, out_buffer, PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height);//SDL—————————-if(SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO | SDL_INIT_TIMER)) {printf( "Could not initialize SDL – %s\n", SDL_GetError()); return -1;} int screen_w=640,screen_h=360;const SDL_VideoInfo *vi = SDL_GetVideoInfo();//Half of the Desktop’s width and height.screen_w = vi->current_w/2;screen_h = vi->current_h/2;SDL_Surface *screen; screen = SDL_SetVideoMode(screen_w, screen_h, 0,0);if(!screen) {printf("SDL: could not set video mode – exiting:%s\n",SDL_GetError());return -1;}SDL_Overlay *bmp; bmp = SDL_CreateYUVOverlay(pCodecCtx->width, pCodecCtx->height,SDL_YV12_OVERLAY, screen); SDL_Rect rect;rect.x = 0;rect.y = 0;rect.w = screen_w;rect.h = screen_h; //SDL End————————int ret, got_picture;AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket));#if OUTPUT_YUV420PFILE *fp_yuv=fopen("output.yuv","wb+"); #endifstruct SwsContext *img_convert_ctx;img_convert_ctx = sws_getContext(pCodecCtx->width, pCodecCtx->height, pCodecCtx->pix_fmt, pCodecCtx->width, pCodecCtx->height, PIX_FMT_YUV420P, SWS_BICUBIC, NULL, NULL, NULL); //——————————SDL_Thread *video_tid = SDL_CreateThread(sfp_refresh_thread,NULL);//SDL_WM_SetCaption("Simplest FFmpeg Grab Desktop",NULL);//Event LoopSDL_Event event;for (;;) {//WaitSDL_WaitEvent(&event);if(event.type==SFM_REFRESH_EVENT){//——————————if(av_read_frame(pFormatCtx, packet)>=0){if(packet->stream_index==videoindex){ret = avcodec_decode_video2(pCodecCtx, pFrame, &got_picture, packet);if(ret < 0){printf("Decode Error.\n");return -1;}if(got_picture){SDL_LockYUVOverlay(bmp);pFrameYUV->data[0]=bmp->pixels[0];pFrameYUV->data[1]=bmp->pixels[2];pFrameYUV->data[2]=bmp->pixels[1];pFrameYUV->linesize[0]=bmp->pitches[0];pFrameYUV->linesize[1]=bmp->pitches[2];pFrameYUV->linesize[2]=bmp->pitches[1];sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);#if OUTPUT_YUV420Pint y_size=pCodecCtx->width*pCodecCtx->height;fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Yfwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //Ufwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V #endifSDL_UnlockYUVOverlay(bmp);SDL_DisplayYUVOverlay(bmp, &rect);}}av_free_packet(packet);}else{//Exit Threadthread_exit=1;break;}}else if(event.type==SDL_QUIT){thread_exit=1;break;}}sws_freeContext(img_convert_ctx);#if OUTPUT_YUV420Pfclose(fp_yuv);#endif SDL_Quit();//av_free(out_buffer);av_free(pFrameYUV);avcodec_close(pCodecCtx);avformat_close_input(&pFormatCtx);return 0;}结果
程序的运行效果如下。这个运行结果还是十分有趣的，会出现一个屏幕“嵌套”在另一个屏幕里面的现象，环环相套。世上没有绝望的处境，只有对处境绝望的人。
