-D

printf("%f",cap.get(CV_CAP_PROP_FRAME_HEIGHT));

для настройки видео рез.

<capture_handle>.set(property_in_caps, value_in_double);

ex, cap.set(CV_CAP_PROP_FRAME_HEIGHT, 720);

ой системы.

з OpenCV:

#if WIN32
  #include <windows.h>
#else
  #include <X11/Xlib.h>
#endif

//...

void getScreenResolution(int &width, int &height) {
#if WIN32
    width  = (int) GetSystemMetrics(SM_CXSCREEN);
    height = (int) GetSystemMetrics(SM_CYSCREEN);
#else
    Display* disp = XOpenDisplay(NULL);
    Screen*  scrn = DefaultScreenOfDisplay(disp);
    width  = scrn->width;
    height = scrn->height;
#endif
}

int main() {
    int width, height;
    getScreenResolution(width, height);
    printf("Screen resolution: %dx%d\n", width, height);
}

попробуй это

#include <stdio.h>
int main()
{
 char *command="xrandr | grep '*'";
 FILE *fpipe = (FILE*)popen(command,"r");
 char line[256];
 while ( fgets( line, sizeof(line), fpipe))
 {
  printf("%s", line);
 }
 pclose(fpipe);
 return 0;
}

В Windows

http://cppkid.wordpress.com/2009/01/07/how-to-get-the-screen-resolution-in-pixels/