cv2.VideoCapture doesn't work within docker container
There might be 2 problems:
1) In your container opencv is not installed properly. To check that do print(ret, frame). If they come (false, None). Then opencv has not installed properly. 
2) The file you are using is corrupted. To check that try to copy any image file (jpg) into the container and use cv2.imread to read the image and then print it. If numpy array comes then while copying your file is not getting corrupted. 
The best option is pull any opencv + python image and then create a container with it. The better option is use dockerfiles of these images to create the container.
I am trying to use cv2.VideoCapture to capture image from a docker container.
import cv2
vid = cv2.VideoCapture('path\to\video')
ret, frame = vid.read()
In terms of the video file,
I have tried 
either mount the file with docker -v
or docker cp to copy the video file into container,
but both with no luck (ret returns False).
Should I add any command when launching the container?
Thanks in advance.