标签：ffmpeg 屏幕录制 libavdevice vc directshow
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）》
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. gdigrab
gdigrab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","640x480",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;
}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，在这里不再详细叙述。
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
* http://blog.csdn.net/leixiaohua1020
*
* 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下则可以使用x11grab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.
*/
#include "stdafx.h"
extern "C"
{
#include "libavcodec/avcodec.h"
#include "libavformat/avformat.h"
#include "libswscale/swscale.h"
#include "libavdevice/avdevice.h"
//SDL
#include "sdl/SDL.h"
#include "sdl/SDL_thread.h"
};
//Output YUV420P
#define OUTPUT_YUV420P 0
//‘1‘ Use Dshow
//‘0‘ Use GDIgrab
#define USE_DSHOW 0
int main(int argc, char* argv[])
{
AVFormatContext *pFormatCtx;
int i, 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 Device
avdevice_register_all();
//Windows
#ifdef _WIN32
#if USE_DSHOW
//Use dshow
//
//Need to Install screen-capture-recorder
//screen-capture-recorder
//Website: http://sourceforge.net/projects/screencapturer/
//
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;
}
#else
//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","640x480",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;
}
#endif
#else
//Linux
AVDictionary* 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","640x480",0);
AVInputFormat *ifmt=av_find_input_format("x11grab");
//Grab at position 10,20
if(avformat_open_input(&pFormatCtx,":0.0+10,20",ifmt,&options)!=0){
printf("Couldn‘t open input stream.（无法打开输入流）\n");
return -1;
}
#endif
if(avformat_find_stream_info(pFormatCtx,NULL)<0)
{
printf("Couldn‘t find stream information.（无法获取流信息）\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.（没有找到视频流）\n");
return -1;
}
pCodecCtx=pFormatCtx->streams[videoindex]->codec;
pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
if(pCodec==NULL)
{
printf("Codec not found.（没有找到解码器）\n");
return -1;
}
if(avcodec_open2(pCodecCtx, pCodec,NULL)<0)
{
printf("Could not open codec.（无法打开解码器）\n");
return -1;
}
AVFrame *pFrame,*pFrameYUV;
pFrame=avcodec_alloc_frame();
pFrameYUV=avcodec_alloc_frame();
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;
//SDL End------------------------
int ret, got_picture;
AVPacket *packet=(AVPacket *)av_malloc(sizeof(AVPacket));
//Output Information-----------------------------
printf("File Information（文件信息）---------------------\n");
av_dump_format(pFormatCtx,0,NULL,0);
printf("-------------------------------------------------\n");
#if OUTPUT_YUV420P
FILE *fp_yuv=fopen("output.yuv","wb+");
#endif
struct 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);
//------------------------------
while(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.（解码错误）\n");
return -1;
}
if(got_picture)
{
sws_scale(img_convert_ctx, (const uint8_t* const*)pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameYUV->data, pFrameYUV->linesize);
#if OUTPUT_YUV420P
int y_size=pCodecCtx->width*pCodecCtx->height;
fwrite(pFrameYUV->data[0],1,y_size,fp_yuv); //Y
fwrite(pFrameYUV->data[1],1,y_size/4,fp_yuv); //U
fwrite(pFrameYUV->data[2],1,y_size/4,fp_yuv); //V
#endif
SDL_LockYUVOverlay(bmp);
bmp->pixels[0]=pFrameYUV->data[0];
bmp->pixels[2]=pFrameYUV->data[1];
bmp->pixels[1]=pFrameYUV->data[2];
bmp->pitches[0]=pFrameYUV->linesize[0];
bmp->pitches[2]=pFrameYUV->linesize[1];
bmp->pitches[1]=pFrameYUV->linesize[2];
SDL_UnlockYUVOverlay(bmp);
rect.x = 0;
rect.y = 0;
rect.w = screen_w;
rect.h = screen_h;
SDL_DisplayYUVOverlay(bmp, &rect);
//Delay 40ms
SDL_Delay(40);
}
}
av_free_packet(packet);
}
sws_freeContext(img_convert_ctx);
#if OUTPUT_YUV420P
fclose(fp_yuv);
#endif
SDL_Quit();
av_free(out_buffer);
av_free(pFrameYUV);
avcodec_close(pCodecCtx);
avformat_close_input(&pFormatCtx);
return 0;
}
#define OUTPUT_YUV420P 0
注：
本工程包含两个基于FFmpeg的libavdevice的例子：
simplest_ffmpeg_grabdesktop：屏幕录制。
simplest_ffmpeg_readcamera：读取摄像头。
标签：ffmpeg 屏幕录制 libavdevice vc directshow
原文地址：http://blog.csdn.net/leixiaohua1020/article/details/39706721
