opencv VideoWriter under OSX producing no output

Question

I am trying to create a video from the python wrapper for OpenCV under OSX. I am using python 2.7.1, opencv 2.3.1a, and the python wrappers from willowgarage that come with that version of opencv. I have:

import cv,cv2 w = cv2.VideoWriter('foo.avi', cv.FOURCC('M','J','P','G'), 25, (100,100)) for i in range(100):     w.write(np.ones((100,100,3), np.uint8)) 

OpenCV says

WARNING: Could not create empty movie file container. Didn't successfully update movie file. ... [ 100 repetitions] 

I'm not sure what to try next

Answer 1

There are many outdated and incorrect online guides on this topic-- I think I tried almost every one. After looking at the source QTKit-based implementation of VideoWriter on Mac OSX, I was finally able to get VideoWriter to output valid video files using the following code:

fps = 15 capSize = (1028,720) # this is the size of my source video fourcc = cv2.cv.CV_FOURCC('m', 'p', '4', 'v') # note the lower case self.vout = cv2.VideoWriter() success = self.vout.open('output.mov',fourcc,fps,capSize,True)  

To write an image frame (note that the imgFrame must be the same size as capSize above or updates will fail):

self.vout.write(imgFrame)  

When done be sure to:

vout.release()  self.vout = None 

This works for me on Mac OS X 10.8.5 (Mountain Lion): No guarantees about other platforms. I hope this snippet saves someone else hours of experimentation!

Answer 2

I am on macOS High Sierra 10.13.4, Python 3.6.5, OpenCV 3.4.1.

The below code (source: https://www.learnopencv.com/read-write-and-display-a-video-using-opencv-cpp-python/) opens the camera, closes the window successfully upon pressing 'q', and saves the video in .avi format.

Note that you need to run this as a .py file. If you run it in Jupyter Notebook, the window hangs when closing and you need to force quit Python to close the window.

import cv2 import numpy as np   # Create a VideoCapture object cap = cv2.VideoCapture(0)   # Check if camera opened successfully if not cap.isOpened():    print("Unable to read camera feed")   # Default resolutions of the frame are obtained.The default resolutions are system dependent. # We convert the resolutions from float to integer. frame_width = int(cap.get(3)) frame_height = int(cap.get(4))   # Define the codec and create VideoWriter object.The output is stored in 'outpy.avi' file. out = cv2.VideoWriter('outpy.avi',cv2.VideoWriter_fourcc('M','J','P','G'), 10, (frame_width,frame_height))   while True:   ret, frame = cap.read()     if ret:            # Write the frame into the file 'output.avi'     out.write(frame)       # Display the resulting frame         cv2.imshow('frame',frame)       # Press Q on keyboard to stop recording     if cv2.waitKey(1) & 0xFF == ord('q'):       break     # Break the loop   else:     break    # When everything done, release the video capture and video write objects cap.release() out.release()   # Closes all the frames cv2.destroyAllWindows()