In order to support 4K, you need to use HEVC as target codec.
(while using AVC for 4K is theoretically possible, the support in actual player devices is actually not that great)
So, I suggest, you back this request first: Transcode to HEVC/x265
Suffice to say that doing so will require your server to have hardware encoding support for HEVC. Even today’s most powerful CPUs cannot sensibly encode to HEVC in realtime.
