libavdevice/v4l2.c:524: error: Uninitialized Value
  The value read from fps.den was never initialized.

libavdevice/v4l2.c:524:9: 
522. 
523.     if (fps.num && fps.den) {
524.         av_log(s1, AV_LOG_DEBUG, "Setting time per frame to %d/%d\n",
             ^
525.                fps.den, fps.num);
526.         tpf->numerator   = fps.den;
