Writing an mp4 video using python opencv

Question

I want to capture video from a webcam and save it to an mp4 file using opencv. I found example code on stackoverflow (below) that works great. The only hitch is that I'm trying to save it as mp4, not avi. Part of what I don't get is that the 'XVID' argument passed to the FOURCC writer is supposed to be, I think, an mp4 codec (from this link). If I change the filename to 'output.mp4' it tells me that the tag is invalid, so I have to believe that the XVID codec is actually making an avi file. Is this a stupid question? How do I write to an mp4?

I have found links showing how to convert an avi to an mp4 after the fact but that seems inefficient. Seems like I should be able to do it during the initial write.

import numpy as np import cv2  cap = cv2.VideoCapture(0)  # Define the codec and create VideoWriter object fourcc = cv2.cv.CV_FOURCC(*'XVID') out = cv2.VideoWriter('output.avi',fourcc, 20.0, (640,480))  while(cap.isOpened()):     ret, frame = cap.read()     if ret==True:         frame = cv2.flip(frame,0)          # write the flipped frame         out.write(frame)          cv2.imshow('frame',frame)         if cv2.waitKey(1) & 0xFF == ord('q'):             break     else:         break  # Release everything if job is finished cap.release() out.release() cv2.destroyAllWindows() 

Answer 1

This worked for me.

self._name = name + '.mp4' self._cap = VideoCapture(0) self._fourcc = VideoWriter_fourcc(*'MP4V') self._out = VideoWriter(self._name, self._fourcc, 20.0, (640,480)) 

Answer 2

What worked for me was to make sure the input 'frame' size is equal to output video's size (in this case, (680, 480) ).

http://answers.opencv.org/question/27902/how-to-record-video-using-opencv-and-python/

Here is my working code (Mac OSX Sierra 10.12.6):

cap = cv2.VideoCapture(0) cap.set(3,640) cap.set(4,480)  fourcc = cv2.VideoWriter_fourcc(*'MP4V') out = cv2.VideoWriter('output.mp4', fourcc, 20.0, (640,480))  while(True):     ret, frame = cap.read()     out.write(frame)     cv2.imshow('frame', frame)     c = cv2.waitKey(1)     if c & 0xFF == ord('q'):         break  cap.release() out.release() cv2.destroyAllWindows() 

Note: I installed openh264 as suggested by @10SecTom but I'm not sure if that was relevant to the problem.

Just in case:

brew install openh264