How can I redirect OpenCV backend errors to a custom logger?

Frontend and Backend Development
1

OpenCV camera scanning shows backend warnings. How do I capture these errors and send them to a custom logger? See the example below:

import cv2

def detect_sources(limit=5):
    sources = []
    for i in range(limit):
        custom_log.debug(f'Checking source {i}')
        cap = cv2.VideoCapture(i, cv2.CAP_MSMF)
        if cap.isOpened():
            sources.append(i)
            cap.release()
    return sources
2

The solution I found involves overriding the default OpenCV logging mechanism by redirecting output streams rather than relying solely on the library’s built-in error handling. An effective approach is to capture standard error (stderr) and then pass that output to a custom logging handler. This can be done by temporarily replacing sys.stderr with an object that writes to your logger. This method has been robust in my projects. Another variant is to use a subprocess with the appropriate redirections if the integration of internal logging proves too cumbersome to modify directly.