This is nice, but has too many moving parts and ffmpeg-like approaches are _not_ the way to go for low-end desktop streaming--I tried doing that in unicast and multicast scenarios quite a few times, and have a few notes on the results:

https://taoofmac.com/space/hw/raspberry_pi/streaming

Instead, I would have used Xrdp (which also works with xrandr) and the DirectFB RDP client instead, like I did ten years ago:

https://taoofmac.com/space/blog/2013/01/09/2339

Even that far back, it worked _extremely_ well on a single-core Pi, and I suspect it would fly on a Pi 3. I used one recently to build a GPU-accelerated thin client:

https://taoofmac.com/space/blog/2022/08/14/2030

...which I recently took to the next level by using xorgxrdp-glamor on the server side:

https://taoofmac.com/space/blog/2022/10/23/1700

I think DirectFB already supports RemoteFX/GFX AVC:444 and all the other niceties that you get with xorgxrdp-glamor on the server side, and am willing to bet the whole thing would run a lot _faster_ and more efficiently than this solution all around, power and bandwidth-wise.

(this is being written in one such RDP client against a Fedora server, and I have YouTube open with audio streaming to the client... Which also works OK via Wi-Fi)