Forced server transcoding for everything. Ouch. Thought maybe at least mpeg2 or something would play directly.

you probably don't have any media in a format that the hardware decoders support.

and it's 480p. every box i've used in the last two decades could do that on the fly without breaking a sweat.

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.