最简单的基于FFmpeg的AVDevice例子（屏幕录制）

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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）

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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. 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：

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//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;

}

2. dshow

使用dshow抓屏需要安装抓屏软件：screen-capture-recorder

软件地址：http://sourceforge.net/projects/screencapturer/

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：

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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：

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/**

* 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

//Windows

extern "C"

{

#include "libavcodec/avcodec.h"

#include "libavformat/avformat.h"

#include "libswscale/swscale.h"

#include "libavdevice/avdevice.h"

#include "SDL/SDL.h"

};

#else

//Linux...

#ifdef __cplusplus

extern "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)

#define SFM_BREAK_EVENT (SDL_USEREVENT + 2)

int thread_exit=0;

int sfp_refresh_thread(void *opaque)

{

thread_exit=0;

while (!thread_exit) {

SDL_Event event;

event.type = SFM_REFRESH_EVENT;

SDL_PushEvent(&event);

SDL_Delay(40);

}

thread_exit=0;

//Break

SDL_Event event;

event.type = SFM_BREAK_EVENT;

SDL_PushEvent(&event);

return 0;

}

//Show Dshow Device

void 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 Device

void 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;

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.\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.\n");

return -1;

}

#endif

#elif defined linux

//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.\n");

return -1;

}

#else

show_avfoundation_device();

//Mac

AVInputFormat *ifmt=av_find_input_format("avfoundation");

//Avfoundation

//[video]:[audio]

if(avformat_open_input(&pFormatCtx,"1",ifmt,NULL)!=0){

printf("Couldn't open input stream.\n");

return -1;

}

#endif

if(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();

//unsigned char *out_buffer=(unsigned char *)av_malloc(avpicture_get_size(AV_PIX_FMT_YUV420P, pCodecCtx->width, pCodecCtx->height));

//avpicture_fill((AVPicture *)pFrameYUV, out_buffer, AV_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_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, AV_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 Loop

SDL_Event event;

for (;;) {

//Wait

SDL_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 unsigned char* 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_UnlockYUVOverlay(bmp);

SDL_DisplayYUVOverlay(bmp, &rect);

}

}

av_free_packet(packet);

}else{

//Exit Thread

thread_exit=1;

}

}else if(event.type==SDL_QUIT){

thread_exit=1;

}else if(event.type==SFM_BREAK_EVENT){

break;

}

}

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;

}