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• openCV function '.read()' return (False, None) in remote environment

  21 juin 2018, par YQ.Wang

  I’m running a video processing programe in docker on a remote Linux environment. I have some problems with the following code :

  import os
  
  import cv2
  
  os.chdir("/home/test/wyq/object_detection/")
  
  print(os.path.exists("test.mp4"))  # see if the file exists
  
  print(cv2.__version__) #check cv's version
  
  cap = cv2.VideoCapture("test.mp4") 
  
  print(cap.read())

  The result is :

  True
  
  3.3.0
  
  (False, None)

  Which means the mp4 file is definitely there and the version of openCV is fine. But it just can’t read it. The Linux environment has ffmpeg as well :
  

  Here are some information about the OS and python :

  Ubuntu 16.04.3 LTS (GNU/Linux 4.4.0-127-generic x86_64)

  Python 3.5.2 (default, Nov 23 2017, 16:37:01)

  [GCC 5.4.0 20160609] on linux

  I think maybe the problem is about the ffmpeg ? Maybe the opencv failed to use the existing ffmpeg ? But I don’t know how to test and solve it. Could somebody be so kind to give me some advice ? Thank you for your attention.

• cv2.videoCapture() return always false, also skvideo.io.VideoCapture()

  26 juillet 2022, par Selin Gök

  I read nearly all of questions about this subject but I didn't solve it.
I am working on Linux/Mint. I tried to open my webcam (or any video it does not matter) with opencv and read a frame from the video. And I write this code :

  



  import cv2

cap = cv2.VideoCapture(0)

while(True):
    ret, frame = cap.read()
    print ret #It returns always false

    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)

    cv2.imshow('frame',gray)
    if cv2.waitKey(1) & 0xFF == ord('q'):
       break

cap.release()
cv2.destroyAllWindows()


  



  —> I read the problem might can be because of opencv installation. I checked the installation, it seems true. When I write 'pip freeze', the result list contained opencv-python module so I thought the installation is correct and it isn't the reason for my problem.

  



  —> I tried to change the index in videoCapture(0) to -1 and 1, and it again failed.

  



  —> And then, I read that the other cause can be FFmpeg or codec. But I also installed FFmpeg and the problem didn't change.

  



  —> cv2.VideoCapture() didn't give any error but I want to install cv2 module on the Poject>Settings>Project Interpreter, it gave me an error (executed command : pip install cv2) But when I run this command, it gave me this error : Could not find a version that satisfies the requirement cv2 (from versions : ) No matching distribution found for cv2
I checked the cv2 module in my virtualenv and it seems there. (/cv_env/lib/python2.7/site-packages/cv2)

  



  —> I also tried it with "skvideo.io.VideoCapture()" but I failed again.

  



  So, I didn't understand the problem and I am really new in this subject. 
What is the problem ?

  


• VideoCapture always returns False in Python OPENCV [Linux]

  26 octobre 2017, par Daniyal Shahrokhian

  Every time that I use VideoCapture trying to access the frames from a video file, the return value (ret) is false. See the sample code below :

  cap = cv2.VideoCapture('asd.mkv')
  
      vid = []
  
      while True:
  
          ret, img = cap.read()
  
          if not ret: # Always happens
  
              break
  
          vid.append(cv2.resize(img, (171, 128)))

  I have already tried absolutely everything I could find today by googling, including the OpenCV guide and this long issue on Github. Also, I read some solutions involving moving ffmpeg dll files, but that only was in the case of Windows.

  Any ideas ? Because I defenitely ran out of them.