Writing numpy arrays using cv2 VideoWriter

Question

I have a problem with writing a toy example video using opencv2.3.1 VideoWriter, here is how I do it:

writer = cv2.VideoWriter('test1.avi',cv.CV_FOURCC('P','I','M','1'),25,(640,480))
for i in range(1000):
    x = np.random.randint(10,size=(480,640)).astype('uint8')
    writer.write(x)
#del writer (with or without tested)

I tried every possible combination resulting with a 0 bytes file if the extension was mpg, and 5.5kb if it was avi. I should say that some pointed out that I should build the ffmpeg library from source and not apt-get it. Well I did that on a fresh machine based on the help of this site http://vinayhacks.blogspot.com/2011/11/installing-opencv-231-with-ffmpeg-on-64.html. which also presented an error while compiling opencv(the error was related to ffmpeg). Now I am really out of ideas, How to generate a video using OPENCV?

Thanks in advance

Answer 1

VideoWriter has last argument isColor with default value True. So if you change it to False then you can write your 2D arrays.

import cv2
import numpy as np

writer = cv2.VideoWriter('test1.avi', cv2.VideoWriter_fourcc(*'PIM1'), 25, (640, 480), False)
for i in range(100):
    x = np.random.randint(255, size=(480, 640)).astype('uint8')
    writer.write(x)

Answer 2

Which OS are you using? Are you sure your system have PIM1 codec installed?

I use windows, and I can use cv.FOURCC(*"DIB ") for uncompressed video, or use -1 to show a codec dialog.

After install ffdshow, I can use cv.FOURCC(*"ffds") to encode the video by MPEG-4.

Answer 3

Hello I am new to opencv and I had this same problem. It appears that the writer.write(x) Needs x to be an array whit RGB values and not scalars. I solved the issue by doing this:

import cv2
import cv2.cv as cv
import numpy as np

writer = cv2.VideoWriter('test1.avi',cv.CV_FOURCC('P','I','M','1'),25,(640,480))
for i in range(1000):
    x = np.random.randint(255,size=(480,640)).astype('uint8')
    x = np.repeat(x,3,axis=1)
    x = x.reshape(480, 640, 3)
    writer.write(x)

I assume there are cleaner ways to do it but I haven't found any.