Hi,
The pipeline may not be well read due to " " or ' '. There are working samples:
Doesn't work nvv4l2decoder for decoding RTSP in gstreamer + opencv - #3 by DaneLLL
Displaying to the screen with OpenCV and GStreamer - #9 by DaneLLL
You may put the pipeline in " " for a try:
"tcpclientsrc host=10.42.0.118 port=5000 ! gdpdepay ! rtph264depay ! h264parse ! avdec_h264 ! videoconvert ! video/x-raw,format=BGR ! videoconvert ! appsink sync=false"