I am coding OpenCV with Python. I can't figure out how to read a video with cv2.VideoCapture().

It is working fine with my webcam but doesn't return anything not even any error messages when I run the code below:

import numpy as np
import cv2
cap = cv2.VideoCapture('vtest.avi')
while(cap.isOpened()):
    ret, frame = cap.read()
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break
cap.release()
cv2.destroyAllWindows()

For what I did to solve this was:

1.used cap = cv2.VideoCapture("C:\vtest.avi") (nothing happened)

2.copied The opencv_ffmpeg_64.dll to the base location(C:\Python27) even in
the folder called DLLs(C:\Python27\DLLs) but nothing is working .