title: TypeError: Required argument 'mat' (pos 2) not found
body: <p>I have the code below with cv2 . This code is downloaded from <a href="https://github.com/dipakkr/3d-cnn-action-recognition" rel="noreferrer">https://github.com/dipakkr/3d-cnn-action-recognition</a>. I want to use cv2.imshow to visualize the frames of the video it get. But I get the following error. What is the problem?
  I am doubtful of whether this code is really able to read the video as what is returns as the output is an array of zeros. </p>
  
  <pre><code>def video3d(self, filename, color=False, skip=True):
  
          cap = cv2.VideoCapture(filename)
          #ret, frame=cap.read()
          #cv2.imshow('frame', frame)
          nframe = cap.get(cv2.CAP_PROP_FRAME_COUNT) #Returns the specified VideoCapture property  ,,Number of frames in the video file
  
          print (nframe, "nframe")
  
          if skip:
              frames = [x * nframe / self.depth for x in range(self.depth)]
              print (frames, "frameeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees")
  
          else:
              frames = [x for x in range(self.depth)]
              print (frames, "frameseeeeeeeeeeeeeeeeeeeeeeeeeeeeeee2")
  
          framearray = []
  
          for i in range(self.depth):
              cap.set(cv2.CAP_PROP_POS_FRAMES, frames[i])  #Sets a property in the VideoCapture. ,,0-based index of the frame to be decoded/captured next.
              ret, frame = cap.read()
              cv2.imshow(frame)
              print(ret, "reeeeeeeeeeeeeeeeettttttttt")
              print(frame ,"frame issssssssssss:")
              frame = cv2.resize(frame, (self.height, self.width))
              print(frame, "frame222 isssssssssssssss")
              #cv2.imshow(frame)
              if color:
                  framearray.append(frame)
              else:
                  framearray.append(cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY))
  
          cap.release()
          return np.array(framearray)
  
  
  X.append(vid3d.video3d(v_file_path, color=color, skip=skip))
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>    main()
    File "3dcnn.py", line 151, in main
      args.output, args.color, args.skip)
    File "3dcnn.py", line 103, in loaddata
      X.append(vid3d.video3d(v_file_path, color=color, skip=skip))
    File "/home/gxa131/Documents/final_project_computationalintelligence/3d-cnn-action-recognition/videoto3d.py", line 34, in video3d
      cv2.imshow(frame)
  TypeError: Required argument 'mat' (pos 2) not found
  </code></pre>