How can I get one single frame from a video file?

edit

Well, I don't believe there's a seek. You need to do it. For example I do it like this :

#include "opencv2/opencv.hpp"
#include "iostream"

using namespace cv;
using namespace std;
int main(int, char**)
{
    VideoCapture cap ( "tree.avi" ); // open the default camera
    if( ! cap.isOpened () )  // check if we succeeded
        return -1;

    /* Mat edges; */
    namedWindow ( "tree" , 1 );
    double frnb ( cap.get ( CV_CAP_PROP_FRAME_COUNT ) );
    std::cout << "frame count = " << frnb << endl;

    for(;;) {
      Mat frame;
      double fIdx;

      std::cout << "frame index ? ";
      std::cin >> fIdx;
      if ( fIdx < 0 || fIdx >= frnb ) break;
      cap.set ( CV_CAP_PROP_POS_FRAMES , fIdx );
      bool success = cap.read(frame); 
      if ( ! success ) {
    cout << "Cannot read  frame " << endl;
    break;
      }
      /* cap >> frame; // get a new frame from camera */
      imshow("tree", frame);
      if ( waitKey (0) == 27 ) break;
    }
    // the camera will be deinitialized automatically in VideoCapture destructor
    return 0;
}

But, there's some errors I can't explain. The execution is OK 'till you start it with an index at most 100 though the FRAME_COUNT says 451 !? For example, let's tell the first frame to read is #100, next you can read any frame indexed before or after 100. I'd like to fix it. I also try the Haris' code but I met the same bug, i.e. the last frame (#450) isn't read... If you could help me to understand I'll be grateful....

Well, there's no pb ! The test video file was corrupted !!! Thus, you can use the code without trouble.

Hi, You can refer OpenCV documentation about Reading and Writing Images and Video

• Get total frame count using VideoCapture::get by passing the id CV_CAP_PROP_FRAME_COUNT.

• Then using VideoCapture::set set the index to next frame to be captured, note that the index is 0 based.

See below code

 VideoCapture cap("video1.mp4"); 
    if( !cap.isOpened()){
         cout << "Cannot open the video file" << endl;
         return -1;
    }

    double count = cap.get(CV_CAP_PROP_FRAME_COUNT); //get the frame count
    cap.set(CV_CAP_PROP_POS_FRAMES,count-1); //Set index to last frame
    namedWindow("MyVideo",CV_WINDOW_AUTOSIZE);

    while(1)
    {
        Mat frame;
        bool success = cap.read(frame); 
        if (!success){
          cout << "Cannot read  frame " << endl;
          break;
        }
        imshow("MyVideo", frame);
        if(waitKey(0) == 27) break;
    }