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

i've picked 'learning opencv' , have been trying of code examples/exercises. in code snippet, want slider update position each video frame change, reason won't work (the picture freezes following code):

#include "cv.h" #include "highgui.h"  int g_slider_position = 0; cvcapture* g_capture = null;  void ontrackbarslide(int pos) {     cvsetcaptureproperty(g_capture, cv_cap_prop_pos_frames, pos); }  int main(int argc, char** argv) {     cvnamedwindow("the tom 'n jerry show", cv_window_autosize);     g_capture = cvcreatefilecapture(argv[1]);     int frames = (int) cvgetcaptureproperty(         g_capture,          cv_cap_prop_frame_count         );      if (frames != 0)     {         cvcreatetrackbar(             "position",             "the tom 'n jerry show",             &g_slider_position,             frames,             ontrackbarslide             );     }      iplimage* frame;      while (1)     {         frame = cvqueryframe(g_capture);         if (!frame)              break;          cvsettrackbarpos(             "position",              "the tom 'n jerry show",             ++g_slider_position             );          cvshowimage("the tom 'n jerry show", frame);         char c = cvwaitkey(33);         if (c == 27)             break;     }      cvreleasecapture(&g_capture);     cvdestroywindow("the tom 'n jerry show");      return 0; } 

any idea how slider , video work intended?

this actual working code    // program add updating trackbar video  #include <cv.h> #include <highgui.h>   int g_slider_position = 0; cvcapture* video_capture = null;  void ontrackbarslide(int current_frame) {     current_frame = g_slider_position;     cvsetcaptureproperty(video_capture,cv_cap_prop_pos_frames,current_frame); }  int main( int argc, char** argv ) {     cvnamedwindow( "video", cv_window_autosize );     video_capture = cvcreatefilecapture( "crowdy.avi");     int no_of_frames = (int) cvgetcaptureproperty(video_capture,cv_cap_prop_frame_count);     if( no_of_frames!= 0 )      {         cvcreatetrackbar("slider","video",&g_slider_position,no_of_frames,ontrackbarslide);     }      iplimage* frame;      while(1)      {         frame = cvqueryframe( video_capture );         if( !frame ) break;         cvshowimage( "video", frame );         cvsettrackbarpos("slider","video",++g_slider_position);         char c = cvwaitkey(33);         if( c == 27 ) break;     }     cvreleasecapture( &video_capture );     cvdestroywindow( "video" );      return(0); }