OpenCV: cant get framerate from video

I want to get framerate for video but I always get -nan on linux.

VideoCapture video(input);
if (!video.isOpened())  // zakoncz program w przypadku, problemu z otwarciem
{
    exit(0);
}

double fps = video.get(CV_CAP_PROP_FPS);

My openCv version is 2.4.7. The same code works fine on windows.