Personally, I found that if you throw any Nvidia Turing line of GPUs in your server, you can transcode any video file with ease and have it look great (including 4K but careful about HDR content, it will look washed out). I paired an atom CPU with a GTX 1660 and after patching the driver to allow more than 2 video encodes, was able to transcode 5 4K steams at the same time.