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demo program with video recording and gamepad


Well-known member
Dec 15, 2019
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Vienna. Austria
Hi everyone,
I am fiddling around with video and with the gamepad and I am slowly getting there. My script is in a state which is usable. You may get some ideas from it and I am looking forward for hints.
I started from the Tello3 demo and enlarged it step by step. I work with Python3 under Windows.

With all the official apps I got glitches in the video. It means that movements are shown jerky. This disturbs me a lot. I tried a range extender which seems to make it better but not satisfactory. In my script I just do basic stuff with opencv and there are no glitches. Very fine, so far.

Just adding video and flying Tello by typing commands like "forward 100" is not satisfactory, so I added joystick support. I am testing with a rather inexpensive gamepad (STRIKE NX) and the inputs library. Gamesir t1d won't connect to the PC.
If no gamepad is found, the gamepad task just terminates and you can fly Tello by typing commands.

Room for improvement:
  • Communication does not start reliably. If you see an "OK", it is OK. If not, quit and restart.
  • Tons of messages from opencv/ffmpeg indicating that there are no (or not enough) key frames. These blue and red ones. Maybe there is a way to increase a timeout in opencv.
  • Both input() and inputs.get_gamepad() are blocking. When you quit the program via keyboard you need to move a joystick. Vice versa, when you quit the program via joystick button, you need to press enter.
  • Video can be started and stopped only once, then the video task terminates
  • I never learned object oriented programming and it looks like I never will.
  • If you don't enter a command for 15 seconds (not very likely), Tello will land automatically.

Okay, and here is the script, have some fun with it!

import threading
import socket
import sys
import time
import os
import inputs # for gamepad

# import opencv 4.2.0
import cv2

def recv():
    global TimeSent
    global Ready
    global Running
    global DataDecoded
    print ("Tello recv task started")
    count = 0
    while Running:
        RecvError = False
            data, server = sock.recvfrom(1518)
        except Exception as e:
            RecvError = True
            if (str(e) == 'timed out'):
                print (".", end = "") # python2 users, please remove this line
                print ('\n------------------- Exception: ' + str(e) + '\n')
        if (not RecvError):
            DataDecoded = data.decode(encoding="utf-8")
            Ready = True

    print ("recv ended")
def rcCommand (RcArray):
    '''create a command like rc 100 100 100 100 from an array of 4 integers'''
    RcCommand = 'rc'
    for Count in range (0,4):
        if (RcArray[Count] > 100):
            RcArray[Count] = 100
        if (RcArray[Count] < -100):
            RcArray[Count] = -100
        RcCommand = RcCommand + ' ' + str(RcArray[Count])
    # print (RcCommand)
    return (RcCommand)

def pad():
    global Running
    global RunningVideo
    global Rc
    global sock
    global Ready
    pads = inputs.devices.gamepads
    if (len(pads) > 0):
        print ("found gamepad" + str(pads[0]))
        while (Running):
            msgPad = ''
            events = inputs.get_gamepad()
            for event in events:
                # print(event.ev_type, event.code, event.state)
                msgPad = "" # preset
                if (event.ev_type == "Absolute"):
                    # print (event.code)
                    stickVal = int(int (event.state) / 327) # / 32767 * 100
                    if (event.code == "ABS_X"):
                        Rc[3] = stickVal
                    elif (event.code == "ABS_Y"):
                        Rc[2] = stickVal
                    elif (event.code == "ABS_RX"):
                        Rc[0] = stickVal
                    elif (event.code == "ABS_RY"):
                        Rc[1] = stickVal
                    msgPad = rcCommand (Rc)
                elif (str(event.ev_type) == "Key"):
                    if (event.code == "BTN_NORTH"):
                        if (str(event.state) == "1"):
                            msgPad = "takeoff"
                            Ready = False
                    elif (event.code == "BTN_SOUTH"):
                        if (str(event.state) == "1"):
                            msgPad = "land"
                            Ready = False
                    elif (event.code == "BTN_WEST"):
                        if (str(event.state) == "1"):
                            ### something to do with this button
                    elif (event.code == "BTN_EAST"):
                        if (str(event.state) == "1"):
                            ### something to do with this button
                    elif (event.code == "BTN_TL"):
                        if (str(event.state) == "1"):
                                RunningVideo = True
                                print ("starting video")
                    elif (event.code == "BTN_TR"):
                        if (str(event.state) == "1"):
                                RunningVideo = False
                                print ("stopping video")
                    elif (event.code == "BTN_START"):
                        if (str(event.state) == "1"):
                            msgPad = "rc -100 -100 -100 100"
                            print ("starting motors")
                    elif (event.code == "BTN_SELECT"):
                        if (str(event.state) == "1"):
                            msgPad = "emergency"
                            Running = False

            if (msgPad != ""):
                if not 'rc' in msgPad:
                    print (msgPad)
                msgPad = msgPad.encode(encoding="utf-8")
                sent = sock.sendto(msgPad, tello_address)

        print ("No gamepad found")
    print ("pad task ended")


def video():
    global out
    global displayVideo
    global writeVideo
    global RunningVideo
    global Running

    print ("video task started")
    # wait for frame
    ret = False
    # scale down
    scale = 1
    # wait until video is started by user
    while Running and not RunningVideo:
        time.sleep (1)
    if not Running:
        print ("video task ended")
    time.sleep(3)    # give tello some time to start video stream

    print ("starting video window")
    telloVideo = cv2.VideoCapture("udp://@")
    if (telloVideo.isOpened() == False):
        print("Unable to read camera feed")
        time.sleep(3)    # give ffmpeg some time to analyze video stream
        frame_width  = int(telloVideo.get(cv2.CAP_PROP_FRAME_WIDTH))
        frame_height = int(telloVideo.get(cv2.CAP_PROP_FRAME_HEIGHT))
        frame_fps    =     telloVideo.get(cv2.CAP_PROP_FPS)
        print (frame_width, ' x ', frame_height, ' ', frame_fps, 'fps' )
        if writeVideo:
            # find a filename which doesn't yet exist
            found = False
            count = 0
            while (not found):
                filenameToWrite = 'telloVideo' + str(count).zfill(3) + '.avi'
                # filenameToWrite = os.path.join (pathToWrite, filenameToWrite)
                if (os.path.exists(filenameToWrite)):
                    count = count + 1
                    found = True
            fourcc = cv2.VideoWriter_fourcc(*'XVID')
            # fourcc = cv2.VideoWriter_fourcc(*'MJPG')
            out = cv2.VideoWriter(filenameToWrite, fourcc, frame_fps, (frame_width,frame_height))

        videoInterval = 1 / frame_fps
        timeNextFrame = time.time() + videoInterval
        timeStart = time.time()
        numFramesReceived = 0
        numFramesWritten = 0
        numGlitches = 0

        while Running and RunningVideo:
            # Capture frame-by-frame
            ret, frame = telloVideo.read()
                # Our operations on the frame come here
                numFramesReceived = numFramesReceived + 1
                if writeVideo:
                    numFramesWritten = numFramesWritten + 1
                    timeNextFrame = timeNextFrame + videoInterval
                    if (time.time() > timeNextFrame):
                        numGlitches = numGlitches + 1

                # Display the resulting frame
                if (displayVideo):
                    if (scale != 1):
                        height , width , layers =  frame.shape
                        frame = cv2.resize(frame, (new_w, new_h)) # <- resize for improved performance
                    cv2.waitKey(1)    # this is essential, otherwise cv2 won't show anything!
        timeVideo = time.time() - timeStart
        # When everything is done, clean up
        # do some statistics
        print ("time: ", timeVideo)
        print (numFramesReceived, "frames received, ", numFramesReceived/timeVideo, " fps")
        print (numFramesWritten,  "frames written",    numFramesWritten/timeVideo,  " fps")
        print (numGlitches, " glitches")

        print ("video task ended")
host = ''
port = 9000
locaddr = (host,port)

# Create a UDP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.settimeout (1)

tello_address = ('', 8889)

TimeSend = 0
Ready = True
Rc = [0,0,0,0]

print ('\r\n\r\nTello Python3 Demo.\r\n')
print ('Tello: command takeoff land flip forward back left right \r\n       up down cw ccw speed speed? battery?\r\n')
print ('end -- quit demo.\r\n')

Running = True
RunningVideo = False
DataDecoded = ""
out = None
displayVideo = True
writeVideo = True

#recvThread create
recvThread = threading.Thread(target=recv)

#videoThread create
videoThread = threading.Thread(target=video)

# padThread create
padThread = threading.Thread(target=pad)

msg = 'command'

while Running:
    if (msg == ''):
        msg = input(">")

    if 'video' in msg:
        RunningVideo = True;
        msg = 'streamon'
    elif 'start' in msg:
        msg = "rc -100 -100 -100 100"    # start motors

    elif 'end' in msg:
        print ('...')
        Running = False
        RunningVideo = False
        msg = ''

    if (msg != ''):
        # Send data
        msg = msg.encode(encoding="utf-8")
        sent = sock.sendto(msg, tello_address)
        TimeSent = time.time()
        print (str(sent) + ' bytes sent')
        msg = ''

TimeShutdown = 2
print ("Will shut down in " + str(TimeShutdown) + " seconds")
time.sleep (TimeShutdown) # give recv task some time to end
An update:

In the "room for improvement" I forgot to mention the delay. It can be quite long. This script is definitely not suitable for FPV flying. Maybe the jerky video in other apps comes from sacrificing frames in order to keep up with real time.

The recorded video was pretty good, I expected that I would need only a little fine-tuning. The picture seems to be compressed too much. When I fly over a meadow with many wildflowers, I lose details (mowing the grass would be an option to reduce details).
I fiddled around with the script, adding some improvements which should not be critical, in my opinion. Added expo to the sticks, moved the keyboard input to a separate thread, added the daemon flag to joystick and keyboard threads so the program terminates without endlessly waiting for an input, and so on.

The result was a disaster. With the slightest movement, the picture was filled with block artefacts. Luckily I had this post which I used as a backup and restored the version you see here.

My computer is not that slow, maybe python slows it down. I think about moving to C++. Of course, when you want to do good videos, there are other quadrocopters on the market which can do ist out of the box. On the other hand, Tello is such a nice little toy and I love programming.
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