Intel ARC 380's are ideal at 4k realtime transcoded streams. And theyre cheap as well.
You could probably do a sticky round robin reverse proxy with a few backends doing transcode.
The biggest issue is bandwidth, but you probably knew that.
Even better is a passive cooled GPU like the Palit 3050 KalmX https://www.palit.com/palit/vgapro.php?id=5147 Too bad they are not producing them anymore
Even better is a passive cooled GPU like the Palit 3050 KalmX https://www.palit.com/palit/vgapro.php?id=5147 Too bad they are not producing them anymore