Update datasets.py (#3216)

utils/datasets.py

@@ -284,7 +284,7 @@ class LoadStreams:  # multiple IP or RTSP cameras
             assert cap.isOpened(), f'Failed to open {s}'
             w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
             h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
-            self.fps = cap.get(cv2.CAP_PROP_FPS) % 100
+            self.fps = (cap.get(cv2.CAP_PROP_FPS) % 100) or 30.0  # assume 30 FPS if cap gets 0 FPS
             self.frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
 
             _, self.imgs[i] = cap.read()  # guarantee first frame