Writing video with OpenCV + Python + Mac

Question

I keep getting an assertion error when I\'m trying to write frames to video. The error I\'m getting is this:

Traceback (most recent call last):
  File \"Vide         


        

Answer 1

I tried various codecs including 'MJPG' and 'I420' and none of them worked on my Mac OpenCV build. They produced tiny unviewable output files without complaining.

Then I found this page which lists some codecs that worked for me. E.g. 'mp4v' works fine on my Mac and QuickTime is able to play it.

Answer 2

Do some of your frames have different colorspaces or depths? A few observations:

• You have swapped the height and width in your code, is that on purpose?
• Your fourcc should be an integer > 0. See my example below.

I haven't personally generated Quicktime video using OpenCV, but this worked for me generating an uncompressed AVI file. I choose the I420 fourcc using the cv.CV_FOURCC function:

import cv
import sys

# standard RGB png file
path = 'stack.png'
cap = cv.CaptureFromFile(path)
fps = 24
width = int(cv.GetCaptureProperty(cap, cv.CV_CAP_PROP_FRAME_WIDTH))
height = int(cv.GetCaptureProperty(cap, cv.CV_CAP_PROP_FRAME_HEIGHT))
# uncompressed YUV 4:2:0 chroma subsampled
fourcc = cv.CV_FOURCC('I','4','2','0')
writer = cv.CreateVideoWriter('out.avi', fourcc, fps, (width, height), 1)
for i in range(90):
    cv.GrabFrame(cap)
    frame = cv.RetrieveFrame(cap)
    cv.WriteFrame(writer, frame)

Update: Screencapture of VLC playing out.avi:

In Quicktime:

Answer 3

This file in the OpenCV source implies on line #2598 - if this assert fails: "dst.data == dst0.data"

it means that the destination size or type was incorrect