GStreamer reading "Producer Reference Time" from a RTSP h264 stream

Decoding with a modified ffprobe one can get:

ffprobe -show_packets -show_frames -of json <rtspstream of ip camera>

AvPacket:
 "side_data_list": [
     {
         "side_data_type": "Producer Reference Time"
         "wallclock": 213414,
         "flags": 24
     }

I dug for about 10hours inside GStreamer but coulndn't decode this data, let alone make it available for GStreamer API downstream. Would love any tips.

I've compiled GStreamer from source on Ubuntu, ran it with logging on 1000, then crossreferenced function calls visible there to find my way around, tried various sections depay, demux, decode...