Try this, pass your desire video mode in variable "res"
Code:
switch(res)
{
case 13:
video_set(1280, 720, 0, 1);
break;
case 14:
video_set(1280, 768, 0, 1);
break;
case 15:
video_set(1280, 800, 0, 1);
break;
case 16:
video_set(1440, 900, 0, 1);
break;
case 17:
video_set(1680, 1050, 0, 1);
break;
case 18:
video_set(1920, 1080, 0, 1);
break;
case 19:
video_set(1900, 1200, 0, 1);
break;
case 20:
video_set(2560, 1600, 0, 1);
break;
default:
if (res < 6 || res > 12)
{
res = 6;
}
video_switch(res,0,1);
}
if (integer(screen_size.x / screen_size.y * 100) > 133)
{
camera.aspect = (screen_size.x/4)/integer((screen_size.y/3));
}