error: (-2) GStreamer: cannot link elements in function CvVideoWriter_GStreamer::open

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does anyone know how to fix this problem? little clues would be appreciated.

** (ros_exploration:14898): CRITICAL **: gst_missing_encoder_message_new: assertion 'gst_caps_is_fixed (encode_caps)' failed

(ros_exploration:14898): GStreamer-CRITICAL **: gst_element_post_message: assertion 'message != NULL' failed
OpenCV Error: Unspecified error (GStreamer: cannot link elements

    ) in CvVideoWriter_GStreamer::open, file /home/htf/Downloads/opencv-2.4.13.6/modules/highgui/src/cap_gstreamer.cpp, line 1464
    Qt has caught an exception thrown from an event handler. Throwing
    exceptions from an event handler is not supported in Qt. You must
    reimplement QApplication::notify() and catch all exceptions there.

terminate called after throwing an instance of 'cv::Exception'
  what():  /home/htf/Downloads/opencv-2.4.13.6/modules/highgui/src/cap_gstreamer.cpp:1464: error: (-2) GStreamer: cannot link elements
 in function CvVideoWriter_GStreamer::open

Aborted (core dumped)