[Python] Unable to receive vídeo Stream from tello drone

I am writhing a python script in order to communicate to my tello drone via wifi. Once connected with the drone I can send UDP packets to send commands (this works perfectly fine). I want to receive the video stream from the drone via UDP packets arriving at my udp server on port 11111. This is described in the SDK documentation, "https://dl-cdn.ryzerobotics.com/downloads/tello/20180910/Tello%20SDK%20Documentation%20EN_1.3.pdf".


print ('\r\n\r\nTello drone communication tool\r\n')

print("...importing modules...")

import threading
import socket
import sys
import time
import platform
import cv2

print("Modules imported")

print("...Initialiasing UDP server to get video stream....")

drone_videostream = cv2.VideoCapture('udp://@0.0.0.0:11111')

print("Server initialised")

# my local adress to receive UDP packets from tello DRONE
host = ''
port = 9000
locaddr = (host,port)

print("...creation of UDP socket...")
# Create a UDP socket (UDP Portocol to receive and send UDP packets from/to drone)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Got drone port and ip adress from network (explained in official SDK documentation)
tello_address = ('192.168.10.1', 8889)

print("UDP socket created")


sock.bind(locaddr)

width = 320
height = 240


def receiveStream() :
print("...receiving stream...")
while True :
ret, frame = drone_videostream.read()
img = cv2.resize(frame, (width, height))
cv2.imshow("LiveStream", frame)
cv2.waitKey(1)
drone_videostream.release()
cv2.destroyAllWindows()


def receiving():
while True:
try:
data, server = sock.recvfrom(1518)
print(data.decode(encoding="utf-8"))
except Exception:
print ('\nExit . . .\n')
break


print ("...initialiazing connection with tello drone...")

message = "command"
message = message.encode(encoding="utf-8")
sent = sock.sendto(message, tello_address)

print("Connection established")

#create a thread that will excute the receiving() function
receiveThread = threading.Thread(target=receiving)
receiveThread.start()

receiveStreamThread = threading.Thread(target=receiveStream)


while True :
message = input(str("Enter a command :\r\n"))
if message == "streamon" :
message = message.encode(encoding="utf-8")
sent = sock.sendto(message, tello_address)
receiveStreamThread.start()
else :
message = message.encode(encoding="utf-8")
sent = sock.sendto(message, tello_address)




When I send the "streamon" command to the drone, I am unable to read the sended UDP packets. I get the following error :

error: (-215:Assertion failed) !ssize.empty() in function 'cv::resize'


This means that the frames are empty, thus, no image received.

Do you know why I dont receive them ?

Thank you very much for your help in advance, Best

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