stream framerate fix

utils/datasets.py

@@ -284,10 +284,11 @@ def __init__(self, sources='streams.txt', img_size=640, stride=32):
             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))
-            fps = cap.get(cv2.CAP_PROP_FPS) % 100
+            self.fps = cap.get(cv2.CAP_PROP_FPS) % 100
+
             _, self.imgs[i] = cap.read()  # guarantee first frame
             thread = Thread(target=self.update, args=([i, cap]), daemon=True)
-            print(f' success ({w}x{h} at {fps:.2f} FPS).')
+            print(f' success ({w}x{h} at {self.fps:.2f} FPS).')
             thread.start()
         print('')  # newline
 
@@ -306,9 +307,12 @@ def update(self, index, cap):
             cap.grab()
             if n == 4:  # read every 4th frame
                 success, im = cap.retrieve()
+                if not success:
+                    cap.release()
+                    raise StopIteration # This does not correctly throw in a thread
                 self.imgs[index] = im if success else self.imgs[index] * 0
                 n = 0
-            time.sleep(0.01)  # wait time
+            time.sleep(1/self.fps) # wait time 
 
     def __iter__(self):
         self.count = -1