title: GStreamer warning when running OpenCV on Ubuntu
body: <p>I'm trying to get a script running on my raspberry pi (Ubuntu system). Right now, I was just refreshing myself on the basics of opencv, since it's been a little while since I worked with it. So I copy pasted this code straight from the OpenCV website and ran it.</p>
  <pre><code>import numpy as np
  import cv2 as cv
  
  cap = cv.VideoCapture(0)
  
  if not cap.isOpened():
      print(&quot;Cannot open camera&quot;)
      exit()
  
  while True:
      # Capture frame-by-frame
      ret, frame = cap.read()
      
      # if frame is read correctly ret is True
      if not ret:
          print(&quot;Can't receive frame (stream end?). Exiting ...&quot;)
          break
          
      # Our operations on the frame come here
      gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
      
      # Display the resulting frame
      cv.imshow('frame', gray)
      
      if cv.waitKey(1) == ord('q'):
          break
          
  # When everything done, release the capture
  cap.release()
  cv.destroyAllWindows()
  </code></pre>
  <p>Only, running it gave me a solid gray window as a pop-up and threw these errors:</p>
  <pre><code>[ WARN:0] global /usr/local/src/opencv-4.4.0/modules/videoio/src/cap_gstreamer.cpp (1761) handleMessage OpenCV | GStreamer warning: Embedded video playback halted; module v4l2src0 reported: Internal data stream error.
  [ WARN:0] global /usr/local/src/opencv-4.4.0/modules/videoio/src/cap_gstreamer.cpp (888) open OpenCV | GStreamer warning: unable to start pipeline
  [ WARN:0] global /usr/local/src/opencv-4.4.0/modules/videoio/src/cap_gstreamer.cpp (480) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created
  </code></pre>
  <p>The code does still run, since I can close the window by pressing 'q'. But the video streaming part has gone horribly wrong. I don't even know what GStreamer is, let alone what a GStreamer pipeline is. I have no idea how to fix this and haven't found anything online that works.</p>