title: videocapture can't open default camera
body: <p>I tried to open default camera using below code. But it can't. There is a <a href="https://stackoverflow.com/questions/4749498/cant-access-webcam-with-opencv">topic</a> same issue.But I can't find a menu to include HAVE_VIDEOINPUT HAVE_DSHOW. ( I tried cap(0) and cap(1) )</p>
  
  <pre><code>VideoCapture cap(1); // open the default camera
  int iSliderValue1 = 50, iSliderValue2 = 255;
  Mat thresholdImage;
  Mat frame;
  
  
  if(!cap.isOpened())  // check if we succeeded
  {
      cout &lt;&lt; "Webcam cannot open!\n" ;
      return -1;
  }
  </code></pre>
  
  <p>Also,when I run "lsusb" command, the output is below
  <img src="https://i.stack.imgur.com/Dq3vl.png" alt="enter image description here"></p>