Stop a function from writing to stdout

问题:

I have this line in my code:

writer = cv.CreateVideoWriter('video.avi', cv.CV_FOURCC('X','V','I','D'), 30 ,(480,800), 1)

Which outputs to console this:

Output #0, avi, to 'video.avi':
Stream #0:0: Video: mpeg4, yuv420p, 480x800, q=2-31, 24576 kb/s, 90k tbn, 30 tbc

I want to stop it from printing anything to stdout, but keep the possibility to output by myself something further in the code. How can I achieve this?

I tried this, but it didn't worked.

class NullStream:
    def write(self, text):
        pass

sys.stdout = NullStream()
sys.stderr = NullStream()

print "hello" #This doesn't outputs

#This function still outputs to console:
writer = cv.CreateVideoWriter('video.avi', cv.CV_FOURCC('X','V','I','D'), 30 ,(480,800), 1)

sys.stdout = sys.__stdout__
sys.stderr = sys.__stderr__

回答1:

It's not OpenCV that outputs this info. It's FFMPEG (which is called by OpenCV).

You can recompile FFMPEG to disable these debugs.

回答2:

import os
import sys
saved_stdout, saved_stderr = sys.stdout, sys.stderr
sys.stdout = sys.stderr = open(os.devnull, "w")
writer = cv.CreateVideoWriter('video.avi', cv.CV_FOURCC('X','V','I','D'), 30 ,(480,800), 1)
sys.stdout, sys.stderr = saved_stdout, saved_stderr
print 'Now this will print to stdout'

Demo:

>>> import os
>>> import sys
>>> saved_stdout, saved_stderr = sys.stdout, sys.stderr
>>> sys.stdout = sys.stderr = open(os.devnull, "w")
>>> print 'hello world'                     # no output
>>> sys.stderr.write('Invisible Error!\n')  # no ouput
>>> sys.stdout, sys.stderr = saved_stdout, saved_stderr
>>> print 'goodbye world'                   
goodbye world
>>> sys.stderr.write('Error!\n')
Error!