Demo_OpenCV_Webcam.py

#!/usr/bin/env python
import sys
if sys.version_info[0] >= 3:
    import PySimpleGUI as sg
else:
    import PySimpleGUI27 as sg
import cv2 as cv
from PIL import Image
import io
from sys import exit as exit

"""
Demo program that displays a webcam using OpenCV
"""
def main():

    sg.ChangeLookAndFeel('LightGreen')

    # define the window layout
    layout = [[sg.Text('OpenCV Demo', size=(40, 1), justification='center', font='Helvetica 20')],
              [sg.Image(filename='', key='image')],
              [sg.ReadButton('Exit', size=(10, 1), pad=((200, 0), 3), font='Helvetica 14'),
               sg.RButton('About', size=(10,1), font='Any 14')]]

    # create the window and show it without the plot
    window = sg.Window('Demo Application - OpenCV Integration',
                       location=(800,400))
    window.Layout(layout).Finalize()
    
    # ---===--- Event LOOP Read and display frames, operate the GUI --- #
    cap = cv.VideoCapture(0)
    while True:
        button, values = window.ReadNonBlocking()

        if button is 'Exit' or values is None:
            sys.exit(0)
        elif button == 'About':
            sg.PopupNoWait('Made with PySimpleGUI',
                           'www.PySimpleGUI.org',
                           'Check out how the video keeps playing behind this window.',
                           'I finally figured out how to display frames from a webcam.',
                           'ENJOY!  Go make something really cool with this... please!',
                           keep_on_top=True)

        ret, frame = cap.read()

        gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)

        # let img be the PIL image
        img = Image.fromarray(gray)  # create PIL image from frame
        bio = io.BytesIO()  # a binary memory resident stream
        img.save(bio, format= 'PNG')  # save image as png to it
        imgbytes = bio.getvalue()  # this can be used by OpenCV hopefully
        window.FindElement('image').Update(data=imgbytes)

main()

I cannot get this to work under Mojave 10.14.3, PySimpleGUI 3.25, OpenCV 4.0.0.21. No errors show in the console. I see the main window and no video image. If i step through the code, i find that in PySimpleGUI.py on line 1883 in "Update" i am getting an exception saying "an error likely means the window has closed so exit".

I'm trying it with an IP camera, and it only takes the image when pushing the 'about' button. It also displays only one capture, instead of refreshing frames as the while loop iterates. Is there any way to refresh the frames to see it like a video stream?

I changed line 33:
button, values = window.ReadNonBlocking()
to
button, values = window.read(timeout=10)
and it seemed to work fine.