opencv-python: Travis Windows: ImportError: DLL load failed: The specified module could not be found.

Hi, thanks for putting all the work into this! ✨

I have an issue with using opencv-python on Travis Windows instances. Here a simple import cv2 will result in ImportError: DLL load failed: The specified module could not be found.

The problem is: this even happens with opencv-python-headless.

I prepared a small example: https://travis-ci.org/pfaion/travis-opencv-python-test/builds/614589763#L68-L72

More context

I had similar problems when loading manually compiled opencv DLLs on travis. It appears this stems from travis using a Windows server version without GUI support. For manually compiled opencv DLLs I was able to fix this by excluding all Windows GUI options in cmake for OpenCV:

...
    -DWITH_WIN32UI=OFF\
    -DWITH_DSHOW=OFF\
    -DWITH_MSMF=OFF\
    -DWITH_DIRECTX=OFF\
...

Now I tried to use opencv-python-headless but I still can’t load the DLL. I found a thread where other people reported this problem in a travis forum: https://travis-ci.community/t/python-and-opencv-dll-load-fails-every-time/4431/6

Apparently someone already figured out the cause of the problem here:

opencv-python-headless gives the same result because this is a result of OpenCV-Python being linked with AVFoundation support 1.

So I assume this is just a flag that was not turned off correctly for the headless build? I quickly searched through the issues, but could not found it, so here it is 🙂