This can happen if you are using windows 10 N distribution, the N distributions does not come pre installed with windows media feature pack, which is required after OpenCV version 3.4 and onwards.
The preferred solution is to install the feature pack at : https://www.microsoft.com/en-us/software-download/mediafeaturepack
Be careful to choose the version that works with your current version of windows.
If that is not an option, fall back to an earlier version of OpenCV that does not have dll dependencies, you can do that by:pip install opencv-python=3.3.0.9
If the problem still persists try using Dependency walker to find out where specifically your problems stem from and then try fixing them individually.
Since windows rolled out it's N version this problem has been seen at many places, and has many impacts across the windows environment, the fastest way to identify if you have this problem is open youtube in Edge browser, if it says HTML5 media plugin not found, this is the problem.
That should sort the problem, if it doesn't feel free to comment and maybe I can help more.
