Opencv VideoWriter Under OSX Producing No Output

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 ve

Solution 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There are many outdated and incorrect online guides on this topic-- I think I tried almost every one.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!

Solution 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() 

Solution 3:

After trying various options, I found that the frame.size that I was using did not fit the size specified in the VideoWriter: So setting it to the default of my iMac 1280x720 made things work!

import numpy as np
import cv2

cap = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object
fourcc = cv2.VideoWriter_fourcc('m', 'p', '4', 'v')
out = cv2.VideoWriter()
succes = out.open('output.mp4v',fourcc, 15.0, (1280,720),True)
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()

Solution 4:

It's the "size" problem.

import cv2
import time

filename = time.strftime("%m-%d-%H-%M-%S") + '.avi'
fps = 16

cap = cv2.VideoCapture(0)

#in this way it always works, because your get the right "size"
size = (int(cap.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH)),
        int(cap.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT)))
fourcc = cv2.cv.FOURCC('8', 'B', 'P', 'S')     #works, large
out = cv2.VideoWriter(filename, fourcc, fps, size, True)

#in this way, you must set the "size" to your size, 
#because you don't know the default "size" is right or not
#cap.set(3, 640)
#cap.set(4, 480)
#out = cv2.VideoWriter(filename, fourcc, fps, (640, 480), True)

while(cap.isOpened()):
    ret, frame = cap.read()
    if ret == True:
        out.write(frame)
        cv2.imshow('frame', frame)

    if cv2.waitKey(1) & 0xFF == ord('q'):
        break;

else:
    print 'Error...'
    break;

cap.release()
out.release()
cv2.destroyAllWindows()

Solution 5:

Here's a version that works with:

• Python 3.6.3
• OpenCV 3.3.1
• macOS 10.13.1

Installed with brew install opencv.

#!/usr/bin/env python3

import cv2

def main():
    vc = cv2.VideoCapture()
    if not vc.open('input.mp4'):
        print('failed to open video capture')
        return

    fourcc = cv2.VideoWriter_fourcc(*'mp4v')
    # Match source video features.
    fps = vc.get(cv2.CAP_PROP_FPS)
    size = (
        int(vc.get(cv2.CAP_PROP_FRAME_WIDTH)),
        int(vc.get(cv2.CAP_PROP_FRAME_HEIGHT)),
    )

    vw = cv2.VideoWriter()
    if not vw.open('output.mp4', fourcc, fps, size):
        print('failed to open video writer')
        return

    while True:
        ok, frame = vc.read()
        if not ok:
            break

        # Flip upside down.
        frame = cv2.flip(frame, 0)

        # Write processed frame.
        vw.write(frame)

        cv2.imshow('frame', frame)
        if cv2.waitKey(1) & 0xFF == ord('q'):
            break

    vc.release()
    vw.release()
    cv2.destroyAllWindows()

if __name__ == "__main__":
    main()