无法从网络摄像头抓取帧

Question

我正在使用 OpenCV 2.4.6、VS2010 和 Windows 7 64 位。我无法从相机中抓取画面。下面的代码适用于 avi 文件，但无法从相机捕获。谁能帮我，我怎样才能捕捉到框架？提前谢谢.......

这部分其实有问题：

bool bSuccess = cap.read(frame); // 从视频中读取一个新帧

    if (!bSuccess) //if not success, break loop
    {
        cout << "Cannot read a frame from video file" << endl;
        break;
    }

完整的源代码：

#include "opencv2/highgui/highgui.hpp"
#include <iostream>

using namespace cv;
using namespace std;

int main(int argc, char* argv[])
{
    VideoCapture cap(0); // open the video camera no. 0

    if(!cap.isOpened())  // if not success, exit program
    {
        cout << "Cannot open the video file" << endl;
        return -1;
    }

    double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
    double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video

    cout << "Frame size : " << dWidth << " x " << dHeight << endl;

    namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"

    while(1)
    {
        Mat frame;

        bool bSuccess = cap.read(frame); // read a new frame from video

        if (!bSuccess) //if not success, break loop
        {
            cout << "Cannot read a frame from video file" << endl;
            break;
        }

        imshow("MyVideo", frame); //show the frame in "MyVideo" window

        if(waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
        {
            cout << "esc key is pressed by user" << endl;
            break; 
        }
    }
    return 0;
}

Answer 1

您应该在使用 while 循环之前阅读第一帧，如下所示：

Mat frame;
cap.read(frame); 
while(1)
{
    bool bSuccess = cap.read(frame); // read a new frame from video

    if (!bSuccess) //if not success, break loop
    {
        cout << "Cannot read a frame from video file" << endl;
        break;
    }

    imshow("MyVideo", frame); //show the frame in "MyVideo" window

    if(waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
    {
        cout << "esc key is pressed by user" << endl;
        break; 
    }
}