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