OpenCV录屏功能

时间:2022-05-23 蓬蒿人人气:0

OpenCV中VideoCapture和VideoWriter用于读写视频文件，这里的录屏功能用到VideoWriter，用于将捕获的屏幕的每一帧数据保存到视频文件。

VideoWriter写视频文件的步骤

1、bool open(const String& filename, int fourcc, double fps,Size frameSize, bool isColor = true);
2、void write(InputArray image);或者VideoWriter& operator << (const Mat& image);
3、void release();

下列代码用于获取屏幕的截图

int width = GetSystemMetrics(SM_CXSCREEN);
int height = GetSystemMetrics(SM_CYSCREEN);
HDC hdcScreen = GetDC(NULL);
HDC hdcMemDC = CreateCompatibleDC(hdcScreen);
HBITMAP hbmScreen = CreateCompatibleBitmap(hdcScreen, width, height);
 
BITMAPINFO bi;
bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
bi.bmiHeader.biWidth = width;
bi.bmiHeader.biHeight = height;
bi.bmiHeader.biPlanes = 1;
bi.bmiHeader.biBitCount = 24;
bi.bmiHeader.biCompression = BI_RGB;
bi.bmiHeader.biSizeImage = 0;
bi.bmiHeader.biXPelsPerMeter = 0;
bi.bmiHeader.biYPelsPerMeter = 0;
bi.bmiHeader.biClrUsed = 0;
bi.bmiHeader.biClrImportant = 0;
SelectObject(hdcMemDC, hbmScreen);
int lineBytes = ((width * bi.bmiHeader.biBitCount + 31) / 32) * 4;//每行字节数必须是4字节的整数倍
int bmpSize = lineBytes * height;
char* lpbitmap = new char[bmpSize];
BitBlt(hdcMemDC, 0, 0, width, height, hdcScreen, 0, 0, SRCCOPY);
GetDIBits(hdcMemDC, hbmScreen, 0, height, lpbitmap, &bi, DIB_RGB_COLORS);

lpbitmap为屏幕的像素颜色数据，下列代码将lpbitmap作为一帧写到视频中（假设VideoWriter为已正常打开的VideoWriter实例）

cv::Mat bmpMat(height, width, CV_8UC3);
for (int i = 0; i < height; i++)
{
    int srcIndex = (height-i-1) * lineBytes;
    int destIndex = i * width * 3;
    memcpy(&bmpMat.data[destIndex],&lpbitmap[srcIndex],width*3);
}
videoWriter.write(bmpMat);//或videoWriter << bmpMat;

因为lpbitmap中的数据是从左下角到右上角排列，而视频帧图像的数据是从左上角到右下角排列，所以要将数据按行上下翻转，即lpbitmap第一行对应视频图像的最后一行。另外BMP图像数据每行的字节数必须是4字节的整数倍，而写入视频的Mat数据没有这个要求，即每行数据大小是图像实际宽度乘以每个颜色占用的字节数，所以实际每行拷贝的数据是width*3节字。

下面是一段测试代码，这里只录制100帧，实际使用中可通过命令行参数、快捷键或按钮等自行决定开始和结束时间，帧率这里也设为固定的25，其实也应该根据具体形况设定合适的值。最后别忘了将opencv_ffmpegXXX.dll文件放到可执行文件目录下。

#include<windows.h>
#include"opencv2/opencv.hpp"
int main()
{
 
    cv::VideoWriter videoWriter;
    double fps = 25;
    int codec = cv::VideoWriter::fourcc('m', 'p', '4', 'v');
    int width =  GetSystemMetrics(SM_CXSCREEN);
    int height = GetSystemMetrics(SM_CYSCREEN);
 
    time_t seconds = time(0);
    int s = seconds % 60;
    int m = (seconds % 3600) / 60;
    int h = (seconds % (3600 * 24)) / 3600 + 8;
    char timeBuf[128] = { 0 };
    sprintf_s(timeBuf, "CaptureScreen-%d-%d-%d.mp4", h, m, s);
    cv::String filePath = timeBuf;
    videoWriter.open(filePath, codec, fps, cv::Size(width, height), true);
    if (!videoWriter.isOpened())
    {
        return -1;
    }
 
    HDC hdcScreen = GetDC(NULL);
    HDC hdcMemDC = CreateCompatibleDC(hdcScreen);
    HBITMAP hbmScreen = CreateCompatibleBitmap(hdcScreen, width, height);
 
    BITMAPINFO bi;
    bi.bmiHeader.biSize = sizeof(bi.bmiHeader);
    bi.bmiHeader.biWidth = width;
    bi.bmiHeader.biHeight = height;
    bi.bmiHeader.biPlanes = 1;
    bi.bmiHeader.biBitCount = 24;
    bi.bmiHeader.biCompression = BI_RGB;
    bi.bmiHeader.biSizeImage = 0;
    bi.bmiHeader.biXPelsPerMeter = 0;
    bi.bmiHeader.biYPelsPerMeter = 0;
    bi.bmiHeader.biClrUsed = 0;
    bi.bmiHeader.biClrImportant = 0;
    SelectObject(hdcMemDC, hbmScreen);
 
    int lineBytes = ((width * bi.bmiHeader.biBitCount + 31) / 32) * 4;
    int bmpSize = lineBytes * height;
    char* lpbitmap = new char[bmpSize];
    cv::Mat bmpMat(height, width, CV_8UC3);
    for (int i=0;i<100;i++)
    {
        if (BitBlt(hdcMemDC, 0, 0, width, height, hdcScreen, 0, 0, SRCCOPY))
        {
            GetDIBits(hdcMemDC, hbmScreen, 0, height, lpbitmap, &bi, DIB_RGB_COLORS);
            for (int i = 0; i < height; i++)
            {
                int srcIndex = (height-i-1) * lineBytes;
                int destIndex = i * width * 3;
                memcpy(&bmpMat.data[destIndex],&lpbitmap[srcIndex],width*3);
            }
            videoWriter.write(bmpMat);//videoWriter << bmpMat;
        }
    }
    delete[] lpbitmap;
    if (videoWriter.isOpened())
    {
        videoWriter.release();
    }
    return 0;
}

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