How to record video using OpenCV and Python? [duplicate]

Question

I have looked at OpenCV's Python example on how to use VideoCapture and VideoWriter to capture and write out a video file. But I keep getting:

OpenCV Error: Assertion failed (dst.data == dst0.data) in cvCvtColor, file 
/tmp/opencv-n8PM/opencv-2.4.7.1/modules/imgproc/src/color.cpp, line 4422
Traceback (most recent call last):
  File "examples/observer/observer.py", line 17, in <module>
    video_writer.write(frame)
cv2.error: /tmp/opencv-n8PM/opencv-2.4.7.1/modules/imgproc/src/color.cpp:4422: error: 
(-215) dst.data == dst0.data in function cvCvtColor

Cleaned up camera.

Here is the code:

#!/usr/bin/env python import cv2


if __name__ == "__main__":
    # find the webcam
    capture = cv2.VideoCapture(0)

    # video recorder
    fourcc = cv2.cv.CV_FOURCC(*'XVID')  # cv2.VideoWriter_fourcc() does not exist
    video_writer = cv2.VideoWriter("output.avi", fourcc, 20, (680, 480))

    # record video
    while (capture.isOpened()):
        ret, frame = capture.read()
        if ret:
            video_writer.write(frame)
            cv2.imshow('Video Stream', frame)

        else:
            break

    capture.release()
    video_writer.release()
    cv2.destroyAllWindows()

Answer 1

The size of the frames is probably incorrect:

w=int(capture.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH ))
h=int(capture.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT ))
# video recorder
fourcc = cv2.cv.CV_FOURCC(*'XVID')  # cv2.VideoWriter_fourcc() does not exist
video_writer = cv2.VideoWriter("output.avi", fourcc, 25, (w, h))

worked for me

Answer 2

In C++ if you can pass -1 for the codec. Then you can choose the codec by hand from all codecs on your machine. Might be the same in python, i can't find it in the documentation though.

video_writer = cv2.VideoWriter("output.avi", -1, 20, (680, 480))

Try it to make sure that opencv can find XVID on your machine.

Answer 3

I faced similar problem. You should debug if the problem is in frame sizes and colors' depth or in you codec. Try writing empty array into the file:

capSize = (100, 100) # this is the size of my source video
fourcc = cv2.cv.CV_FOURCC('m', 'p', '4', 'v')
out = cv2.VideoWriter('output.mov',fourcc, 1, capSize)
...
out.write(125 * np.ones((100,100,3), np.uint8)) 
...