# python 3.7 
# Version of code that worked with CV2 version 3.4.10.37 
import cv2

...

target_video = "name.mp4"
...
fourcc = cv2.VideoWriter_fourcc('m', 'p', '4', 'v')
outputStream = cv2.VideoWriter(target_video, fourcc, 20.0, (500,500))
...
outputStream.write(frame)

...

outputStream.release()