[ WARN:0] terminating async callback

[nerdfever]

Expected behaviour

Assuming 2 cameras (also gives the error if only one camera):

C:\Users\Dave\data\Code\Python\VideoCapture>python3 test.py
Found camera 0
Found camera 1

Actual behaviour

C:\Users\Dave\data\Code\Python\VideoCapture>python3 test.py
Found camera 0
[ WARN:0] terminating async callback
Found camera 1
[ WARN:0] terminating async callback

Steps to reproduce

import cv2

def countCameras():
    """Returns count of found cameras (not opened yet).
    Brute force - just tries them all till it fails."""

    camCount = 0

    while True:
        cam = cv2.VideoCapture(camCount)

        if cam.isOpened():
            print("Found camera", camCount)
            cam.release()
            camCount += 1

        else:
            return camCount

countCameras()

• operating system

Windows 10 Pro

• architecture (e.g. x86)

x64

• opencv-python version

cv2.version == '4.1.0'

[skvark]

This is a bug in OpenCV in MSMF backend: opencv/opencv#13255

You could try setx OPENCV_VIDEOIO_PRIORITY_MSMF 0 before running your script. However, there's nothing I can do in this repo to fix the issue.

[linchiyu]

Had this issue on opencv4*, 3.4.4
When installed opencv 3.4.2.16 the warning disappeared