Hi!
First, i want to express my sincerest gratitude for that wonderful software! 
About question: just want to know, would it be possible to decode the stream via gpu?
I use Quadro P1000, CUDA 11.7, Driver 515.65.01 and in Caspar configuration use next parameters in «args»:
-format mpegts
-codec:v h264_nvenc
-filter:v format=pix_fmts=yuv420p,fps=50,interlace -flags:v +ilme+ildct
-mpegts_service_type advanced_codec_digital_hdtv
-mpegts_original_network_id 0x1122
-mpegts_transport_stream_id 0x3344
-mpegts_service_id 0x5566
-mpegts_pmt_start_pid 0x1500
-mpegts_start_pid 0x150
-flush_packets 0
-pcr_period 20 -pat_period 0.10 -sdt_period 0.25
-fflags +genpts -mpegts_flags +system_b
-rc:v cbr_ld_hq
-muxrate 11.5M -max_delay 2M -b:v 10.5M -minrate:v 10.5M
-maxrate:v 10.5M -bufsize:v 2M
-g:v 50
-codec:a aac -b:a 192k -filter:a pan=stereo|c0=c0|c1=c1</args>
And in path i use next settings:
<path>udp://some_mcast?pkt_size=1316&localaddr=some_ip&bitrate=11000000&buffer_size=3400000&fifo_size=500000&burst_bits=100000</path>
In result, see that Casparcg use GPU but only for encoding:
enc dec
% %
28 0
29 0
29 0
30 0
Thank you very much!
Peace