ffmpeg gdi录制桌面视频时注意事项

本人之前写了一个博客：ffmpeg录制桌面(自己用gdi抓图)
当时设置的帧率是10，设置的比较低，原因在于，设置高了，1秒钟抓不到对应的图片数量，会导致最终生成文件播放起来，时间变短。比如设置帧率为20，但是由于电脑的分辨率比较高，一秒钟只能抓10帧。则录制一分钟时，会发现，最终播放起来只有30秒。这显然是有问题的。

当然，我们设置帧率为10也不安全，因为电脑由于各种原因，可能一秒钟也抓不了10帧，当然，我们也不能再将帧率往下设置了，太憋屈了。

此时修改frame->pkt_dts可以达到这种效果，比如写文件时，AVStream的时间基是1000，帧率设置为20.
第一帧的pkt_dts设置为0，则第二帧正常应该为50，第三帧为100，…，第20帧的pkt_dts为950，第21帧的pkt_dts为1000.
但是现在出问题了，电脑性能不够，一秒钟只能抓10张图片，则第一帧的pkt_dts设置为0，第二张的设置为100，这样才能保证最后生成的文件播放起来是ok的；但是这样有个不好的结果，就是最终显示的文件的帧率只有10，而不是设置的20。

所以本篇采取在设置帧率的前提下，尽力交付。比如设置帧率为10时，则如果实际能抓到的张数大于10，则进行相应的Sleep；如果实际能抓到的张数小于10，比如8.则dts设置正确即可，最终生成的文件的帧率是8.

代码结构如下：

CaptureScreen.cpp的内容如下：

//#include "stdafx.h"
#include "CaptureScreen.h"CCaptureScreen::CCaptureScreen(void)
{m_hdib = NULL;m_hSavedCursor = NULL;hScreenDC = NULL;hMemDC = NULL;hbm = NULL;m_width = 1920;m_height = 1080;FetchCursorHandle();
}
//
// 释放资源
//
CCaptureScreen::~CCaptureScreen(void)
{if (hbm){DeleteObject(hbm);hbm = NULL;}if (m_hdib){free(m_hdib);m_hdib = NULL;}if (hScreenDC){::ReleaseDC(NULL, hScreenDC);}if (hMemDC) {DeleteDC(hMemDC);}
}//
// 初始化
//
int CCaptureScreen::Init(int iPosX, int iPosY, int iWidth, int iHeight)
{HWND hDeskTop = GetDesktopWindow();RECT rc;GetWindowRect(hDeskTop, &rc);hScreenDC = ::GetDC(NULL);int iSizeX = GetDeviceCaps(hScreenDC, HORZRES);if (hScreenDC == NULL) return 0;hMemDC = ::CreateCompatibleDC(NULL);if (hMemDC == NULL) return 0;m_iXPos = iPosX;m_iYPos = iPosY;m_width = iWidth;m_height = iHeight;if (!m_hdib){m_hdib = (PRGBTRIPLE)malloc(m_width * m_height * 3);//24位图像大小}//位图头信息结构体pbi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);pbi.bmiHeader.biWidth = m_width;pbi.bmiHeader.biHeight = m_height;pbi.bmiHeader.biPlanes = 1;pbi.bmiHeader.biBitCount = 24;pbi.bmiHeader.biCompression = BI_RGB;hbm = CreateCompatibleBitmap(hScreenDC, m_width, m_height);SelectObject(hMemDC, hbm);wLineLen = ((m_width * 24 + 31) & 0xffffffe0) / 8;wColSize = sizeof(RGBQUAD)* ((24 <= 8) ? 1 << 24 : 0);dwSize = (DWORD)(UINT)wLineLen * (DWORD)(UINT)m_height;return 1;
}//抓取屏幕数据
BYTE* CCaptureScreen::CaptureImage()
{VOID*  alpbi = CaptureScreenFrame(m_iXPos, m_iYPos, m_width, m_height);return (BYTE*)(alpbi);
}void* CCaptureScreen::CaptureScreenFrame(int left, int top, int width, int height)
{if (hbm == NULL || hMemDC == NULL || hScreenDC == NULL) return NULL;//BitBlt(hMemDC, 0, 0, width, height, hScreenDC, left, top, SRCCOPY);BOOL bRet = StretchBlt(hMemDC, 0, 0, width, height, hScreenDC, left, top, width, height, SRCCOPY);/*-------------------------捕获鼠标-------------------------------*/{POINT xPoint;GetCursorPos(&xPoint);HCURSOR hcur = FetchCursorHandle();xPoint.x -= left;xPoint.y -= top;ICONINFO iconinfo;BOOL ret;ret = GetIconInfo(hcur, &iconinfo);if (ret){xPoint.x -= iconinfo.xHotspot;xPoint.y -= iconinfo.yHotspot;if (iconinfo.hbmMask) DeleteObject(iconinfo.hbmMask);if (iconinfo.hbmColor) DeleteObject(iconinfo.hbmColor);}/*画鼠标*/::DrawIcon(hMemDC, xPoint.x, xPoint.y, hcur);}//动态分配的内存PRGBTRIPLE hdib = m_hdib;if (!hdib)return hdib;GetDIBits(hMemDC, hbm, 0, m_height, hdib, (LPBITMAPINFO)&pbi, DIB_RGB_COLORS);return hdib;
}//
// 获取窗体鼠标光标
//
HCURSOR CCaptureScreen::FetchCursorHandle()
{if (m_hSavedCursor == NULL){m_hSavedCursor = GetCursor();}return m_hSavedCursor;
}

CaptureScreen.h的代码如下：

#ifndef _CCAPTURE_SCREEN_HH
#define _CCAPTURE_SCREEN_HH#include<time.h>
#include <d3d9.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <windows.h>#include <tchar.h>
#include <winbase.h>
#include <winreg.h>
#include <Strsafe.h>//
// ---抓屏类----
//
class CCaptureScreen
{
public:CCaptureScreen(void);~CCaptureScreen(void);public:/*-----------定义外部调用函数-----------*/int Init(int iPosX, int iPosY, int iWidth, int iHeight);//初始化BYTE* CaptureImage(); //抓取屏幕private:/*-----------定义内部调用函数-----------*/void* CaptureScreenFrame(int, int, int, int);//抓屏HCURSOR FetchCursorHandle(); //获取鼠标光标private:/*-----------定义私有变量-----------*/int m_iXPos;int m_iYPos;int m_width;int m_height;UINT   wLineLen;DWORD  dwSize;DWORD  wColSize;//设备句柄HDC hScreenDC;HDC hMemDC;//图像RGB内存缓存PRGBTRIPLE m_hdib;//位图头信息结构体BITMAPINFO pbi;HBITMAP hbm = NULL;//鼠标光标HCURSOR m_hSavedCursor;};#endif //--_CCAPTURE_SCREEN_HH

FfmpegVideoCaptureWithGdi.cpp的代码如下：

// RecordingScreen.cpp : 定义控制台应用程序的入口点。
////#include "stdafx.h"
#include "CaptureScreen.h"
#include <string>extern "C"
{
#include <libavutil/opt.h>
#include <libavutil/mathematics.h>
#include <libavutil\time.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
#include <libswresample/swresample.h>
#include <libavutil/imgutils.h>
#include <libavcodec/avcodec.h>
#include <libavdevice\avdevice.h>#pragma comment(lib,"avcodec.lib")
#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avutil.lib")
#pragma comment(lib,"avdevice.lib")
#pragma comment(lib,"avfilter.lib")
#pragma comment(lib,"postproc.lib")
#pragma comment(lib,"swresample.lib")
#pragma comment(lib,"swscale.lib")}int g_iWidth = 2880;
int g_iHeight = 1800;
int g_iFrameRate = 30;
//#include <ipp.h>
#include <chrono>std::string time_tSimpleString(time_t t_time)
{tm temptm = *localtime(&t_time);char strOut[64] = { 0 };sprintf(strOut, "%04d-%02d-%02dT%02d-%02d-%02d", temptm.tm_year + 1900, temptm.tm_mon + 1,temptm.tm_mday, temptm.tm_hour, temptm.tm_min, temptm.tm_sec);return (std::string)strOut;
}unsigned char clip_value(unsigned char x, unsigned char min_val, unsigned char  max_val) {if (x > max_val) {return max_val;}else if (x < min_val) {return min_val;}else {return x;}
}//RGB to YUV420
bool RGB24_TO_YUV420(unsigned char *RgbBuf, int w, int h, unsigned char *yuvBuf)
{unsigned char*ptrY, *ptrU, *ptrV, *ptrRGB;memset(yuvBuf, 0, w*h * 3 / 2);ptrY = yuvBuf;ptrU = yuvBuf + w * h;ptrV = ptrU + (w*h * 1 / 4);unsigned char y, u, v, r, g, b;for (int j = h - 1; j >= 0; j--) {ptrRGB = RgbBuf + w * j * 3;for (int i = 0; i < w; i++) {b = *(ptrRGB++);g = *(ptrRGB++);r = *(ptrRGB++);y = (unsigned char)((66 * r + 129 * g + 25 * b + 128) >> 8) + 16;u = (unsigned char)((-38 * r - 74 * g + 112 * b + 128) >> 8) + 128;v = (unsigned char)((112 * r - 94 * g - 18 * b + 128) >> 8) + 128;*(ptrY++) = clip_value(y, 0, 255);if (j % 2 == 0 && i % 2 == 0) {*(ptrU++) = clip_value(u, 0, 255);}else {if (i % 2 == 0) {*(ptrV++) = clip_value(v, 0, 255);}}}}return true;
}DWORD WINAPI ScreenCapThreadProc(LPVOID lpParam)
{CCaptureScreen* ccs = new CCaptureScreen();//int width = GetSystemMetrics(SM_CXSCREEN);//int height = GetSystemMetrics(SM_CYSCREEN);int width = g_iWidth;int height = g_iHeight;ccs->Init(0, 0, width, height);AVFormatContext* avFormCtx_Out;AVCodecContext*  avCodecCtx_Out;AVCodec*  avCodec;AVStream* avStream;AVFrame* frame;AVPacket* packet;int ret = 0;std::string strFileName = "D:\\learn\\ffmpeg\\FfmpegTest\\x64\\Release\\";strFileName += time_tSimpleString(time(NULL));strFileName += ".mp4";const char* filename = strFileName.c_str();ret = avformat_alloc_output_context2(&avFormCtx_Out, NULL, NULL, filename);if (ret < 0){printf("Init avformat object is faild! \n");return 0;}avCodec = (AVCodec *)avcodec_find_encoder(avFormCtx_Out->oformat->video_codec);if (!avCodec){printf("Init avCodec object is faild! \n");return 0;}avCodecCtx_Out = avcodec_alloc_context3(avCodec);if (!avCodecCtx_Out){printf("Init avCodecCtx_Out object is faild! \n");return 0;}avStream = avformat_new_stream(avFormCtx_Out, avCodec);if (!avStream){printf("Init avStream object is faild! \n");return 0;}avCodecCtx_Out->flags |= AV_CODEC_FLAG_QSCALE;avCodecCtx_Out->bit_rate = 4000000;avCodecCtx_Out->rc_min_rate = 4000000;avCodecCtx_Out->rc_max_rate = 4000000;avCodecCtx_Out->bit_rate_tolerance = 4000000;avCodecCtx_Out->time_base.den = g_iFrameRate;avCodecCtx_Out->time_base.num = 1;avCodecCtx_Out->width = width;avCodecCtx_Out->height = height;//pH264Encoder->pCodecCtx->frame_number = 1;avCodecCtx_Out->gop_size = 12;avCodecCtx_Out->max_b_frames = 0;avCodecCtx_Out->thread_count = 4;avCodecCtx_Out->pix_fmt = AV_PIX_FMT_YUV420P;avCodecCtx_Out->codec_id = AV_CODEC_ID_H264;avCodecCtx_Out->codec_type = AVMEDIA_TYPE_VIDEO;av_opt_set(avCodecCtx_Out->priv_data, "b-pyramid", "none", 0);av_opt_set(avCodecCtx_Out->priv_data, "preset", "superfast", 0);av_opt_set(avCodecCtx_Out->priv_data, "tune", "zerolatency", 0);if (avFormCtx_Out->oformat->flags & AVFMT_GLOBALHEADER)avCodecCtx_Out->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;ret = avcodec_open2(avCodecCtx_Out, avCodec, NULL);if (ret < 0){printf("Open avcodec is faild! \n");return 0;}avcodec_parameters_from_context(avStream->codecpar, avCodecCtx_Out);if (!(avFormCtx_Out->oformat->flags & AVFMT_NOFILE)){ret = avio_open(&avFormCtx_Out->pb, filename, AVIO_FLAG_WRITE);if (ret < 0){printf("Open file is faild! \n");return 0;}}ret = avformat_write_header(avFormCtx_Out, NULL);if (ret < 0){printf("write header is faild! \n");return 0;}frame = av_frame_alloc();if (!frame){printf("Init frame is faild! \n");return 0;}frame->format = AV_PIX_FMT_YUV420P;frame->width = width;frame->height = height;LONG64 frameSize = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, width, height, 1);BYTE* outbuffer = new BYTE[frameSize];ret = av_image_fill_arrays(frame->data,frame->linesize,outbuffer,AV_PIX_FMT_YUV420P,width,height, 1);if (ret < 0){printf("av_image_fill_arrays is faild! \n");return 0;}packet = av_packet_alloc();//av_init_packet(packet);if (!packet){printf("packet is faild! \n");return 0;}int frameNumber = 0;int got_packet = 0;DWORD dwBeginTime = ::GetTickCount();for (;;){BYTE* frameimage = ccs->CaptureImage();RGB24_TO_YUV420(frameimage, width, height, outbuffer);DWORD dwCurrTime = ::GetTickCount();int dts = dwCurrTime - dwBeginTime;AVRational millBase;millBase.den = 1000;millBase.num = 1;frame->pkt_dts = frame->pts = av_rescale_q_rnd(dts, millBase, avStream->time_base, (AVRounding)(AV_ROUND_NEAR_INF | AV_ROUND_PASS_MINMAX));frame->pkt_duration = 0;frame->pkt_pos = -1;ret = avcodec_send_frame(avCodecCtx_Out, frame);if (ret < 0)continue;ret = avcodec_receive_packet(avCodecCtx_Out, packet);if (ret < 0)continue;static DWORD dwInitTime = ::GetTickCount();if (packet->size > 0){//av_packet_rescale_ts(packet, avCodecCtx_Out->time_base, avStream->time_base);av_write_frame(avFormCtx_Out, packet);frameNumber++;printf("录入第%d帧....\n", frameNumber);}/*if (frameNumber >= 600){break;}*/DWORD dwCurrentTime = ::GetTickCount();if (dwCurrentTime - dwInitTime > 60000){break;}int dwPassedMillSeconds = dwCurrentTime - dwBeginTime;int dwDiff = frameNumber * 1000 / g_iFrameRate - dwPassedMillSeconds;if (dwDiff > 0){Sleep(dwDiff);}}av_write_trailer(avFormCtx_Out);avformat_free_context(avFormCtx_Out);avcodec_close(avCodecCtx_Out);avcodec_free_context(&avCodecCtx_Out);av_free(avCodec);av_packet_free(&packet);av_frame_free(&frame);return 0;
}int _tmain(int argc, _TCHAR* argv[])
{//av_register_all();//avformat_network_init();avdevice_register_all();HANDLE hThread = CreateThread(NULL, 0, ScreenCapThreadProc, 0, 0, NULL);WaitForSingleObject(hThread, INFINITE);return 0;
}

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ffmpeg gdi录制桌面视频时注意事项

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