handling multiple cameras with OpenCV and multithreading

Question

I'm trying to set up a neural network to work on multiple cameras simultaneously (or almost at least..). First of all i'm trying to get to stream 2 cameras at once with OpenCV and the python threading module.

I've come up with this code:

import cv2
import threading
import queue

def multistream(stream, q):
    ret, frame = stream.read()
    q.put(frame)

if __name__ == "__main__":
   camlink1 = "rtsp://......link1"
   camlink2 = "rtsp://......link2"
   stream1 = cv2.VideoCapture(camlink1)
   stream2 = cv2.VideoCapture(camlink2)
   print("stream is opened")
   while True:
      q = queue.Queue()
      cam1 = threading.Thread(target=multistream, args=(stream1, q))
      cam2 = threading.Thread(target=multistream, args=(stream2, q))
      cam1.start()
      cam2.start()
      cam1.join()
      cam2.join()
      while not q.empty():
          cv2.imshow("video", q.get())

The problem is that cv2.imshow shows an empty window instead of the frame while, if i add to the code print(q.get()), it prints the mats of which the frame is made, so the frame is correctly returned from the multistream function to the main thread. What's the correct fix for this?