OpenCV - getting the slider to update its position during video playback

Question

I\'ve picked up \'Learning OpenCV\' and have been trying some of the code examples/exercises. In this code snippet, I want to get the slider to update its position with each

Answer 1

This seems a bit complicated to me. I used the cvGetCaptureProperty(g_capture, CV_CAP_PROP_POS_FRAMES) call to retrieve the current frame and used this to update the slider.

The callback function is then used just to change the position within g_capture.

So the call back is:

//Call back for slider bar
void onTrackbarSlide(int pos) {
    cvSetCaptureProperty(g_capture, CV_CAP_PROP_POS_FRAMES, pos);
}

And the loop is:

IplImage* frame; //Frame grabbed from video
while(1) {
    frame = cvQueryFrame( g_capture );
    if (!frame ) break;
    cvShowImage( "Example2", frame );

    g_frame_count = (int) cvGetCaptureProperty(g_capture, CV_CAP_PROP_POS_FRAMES);

    cvSetTrackbarPos("Position","Example2", g_frame_count);

    char c = cvWaitKey(33);
    if ( c == 27 ) break;
}

Where the g_ variables are global.