title: GStreamer-CRITICAL **: gst_element_make_from_uri: assertion 'gst_uri_is_valid (uri)' failed
body: <p>I am in Ubuntu 16.04 using OpenCV 3.1 in Python. I can run this fine for a large number of videos however in this particular video it fails. I am using XVID as coded. The URI seems to be correct so I'm at a loss here...</p>
  
  <p>Below is the full error (I know some context may be needed, but the path provided for the file is correct. I have tried putting a space at the end as some other answer suggested and it didn't work.</p>
  
  <pre><code>(240, 320, 3)
  Converting all images into a video...
  v_HandStandPushups_g01_c01
  ['', 'media', 'pedro', 'actv3', 'UCF101', 'videos', 'HandstandPushups']
  Height: 224 Width: 224 FPS: 25.0
  /media/pedro/actv3/UCF101/pose/HandstandPushups/v_HandStandPushups_g01_c01_pose.avi
  /media/pedro/actv3/UCF101/pose/HandstandPushups/v_HandStandPushups_g01_c01_joints.npy
  
  (python:1923): GStreamer-CRITICAL **: gst_element_make_from_uri: assertion 'gst_uri_is_valid (uri)' failed
  GStreamer Plugin: Embedded video playback halted; module filesink0 reported: Could not open file "/media/pedro/actv3/UCF101/pose/HandstandPushups/v_HandStandPushups_g01_c01_pose.avi" for writing.
  GStreamer Plugin: Embedded video playback halted; module filesink0 reported: GStreamer error: state change failed and some element failed to post a proper error message with the reason for the failure.
  OpenCV Error: Unspecified error (GStreamer: cannot put pipeline to play
  ) in CvVideoWriter_GStreamer::open, file /home/pedro/opencv/modules/videoio/src/cap_gstreamer.cpp, line 1530
  Traceback (most recent call last):
    File "process_video.py", line 133, in &lt;module&gt;
      main()
    File "process_video.py", line 130, in main
      _process_dataset()
    File "process_video.py", line 119, in _process_dataset
      computePose(videos)
    File "process_video.py", line 101, in computePose
      video = cv2.VideoWriter(poseimg_output_name, fourcc, vidcap.get(cv2.CAP_PROP_FPS), (width,height), True)
  cv2.error: /home/pedro/opencv/modules/videoio/src/cap_gstreamer.cpp:1530: error: (-2) GStreamer: cannot put pipeline to play
   in function CvVideoWriter_GStreamer::open
  </code></pre>
  
  <p><strong>EDIT</strong>: Solution was that I was writing to a non-existent folder. Check your paths very carefully (they are case-sensitive).</p>