I am not 100% sure (I messed around, so not totally sure what the default was), but I think the default gstreamer source url in Mission Planner does not work.
You can set the gstreamer source URL by right-clicking in the HUD, then “Video”->“Set GStreamer Source”. (see picture below)
I believe the original is something like
rtspsrc location=rtsp://192.168.1.133:8554/video1 ! application/x-rtp ! rtpjpegdepay ! videoconvert ! video/x-raw,format=BGRA ! appsink name=outsink
but this does not work.
Based on something posted by Michael Oborne here, I successfully tried
udpsrc port=5600 buffer-size=90000 ! application/x-rtp ! rtph264depay ! avdec_h264 ! queue leaky=2 ! videoconvert ! video/x-raw,format=BGRA ! appsink name=outsink sync=false
I don’t know what most of these parameters actually mean, but it works just fine with this source url, and the command
c:\gstreamer\1.0\msvc_x86\bin>gst-launch-1.0.exe udpsrc port=5500 ! h264parse ! rtph264pay ! udpsink host=127.0.0.1 port=5600
in openhd-settings-1.txt for the ground station.