Realistic to have 4k security camera with Motioneye addon on a RPi 4B?

Running HA core-2022.2.7 with Home Assistant OS on a RPi 4b (2GB ram, 5GHz quad core ARM Cortex-A72)

I have the addon motionEye 0.11.0 installed and this is being reported in the addon:
motionEye Version 0.42.1
Motion Version 4.3.2
OS Version Linux 5.10.92-v7

I have a HikVision clone (namely Anpviz IPC-D383WD-S) that can render a 4k primary stream as well as a 480p secondary stream. My goal is to do motion detection using the 480p stream and perform a save on motion detect with a movie passtrough on the 4k H265 stream to my network attached storage on my router (SSD), all is wired gigabit.

I can connect both primary and secondary streams in home assistant. All is well when I have the primary stream set to 720p 5FPS; ram usage is 900MB/1870MB and CPU happily hovers around 30%.

However CPU usage and RAM usage is becoming sky high when I set the cam stream at 4k, no matter the frame rate. RAM usage is > 1500MB/1870MB and CPU is roughly maxed out at 90-95%. The video becomes lagged, and is behind real time the more the streams runs.

I have nothing enabled besides the “video device”; nothing is connected to the video in HA. “Video Streaming” is not enabled; so no re-coding is being done. “Motion detection” is not even activated at this point. There are no “overlay”, no recording being made at this moment.

Am I asking too much to the Pi ? I was under the impression the Pi could at least hardware decode the H265 stream, but it seems it is all done in software.

Is there anything I can do, besides forget the 4k stream and perform the motion detect/saving in 720p?