Update app.py

app.py

@@ -136,7 +136,7 @@ def infer(url_in,interpolation,fps_output):
       if ret == False:
         break
       next = cv2.cvtColor(frame2, cv2.COLOR_RGB2GRAY)
-      flow = cv2.calcOpticalFlowFarneback(prvs, next, None, 0.5, 3, 15, 3, 5, 1.2, 0)
+      cv2.calcOpticalFlowFarneback(prvs, next, flow, 0.5, 3, 15, 3, 5, 1.2, 0)
       alpha = 1.0/len(frames_list)
       beta = (1.0 - alpha)
       res = cv2.addWeighted(flow, alpha, res, beta, 0.0)