It means get clients that support more file formats without transcoding. TVs rarely support more than the bare minimum, do ideally you'd want a more fully featured client like an Nvidia Shield or an AppleTV.
Also things like subtitles (or the wrong type of subtitles) can cause transcoding, so again making sure you are using the correct options or upgrade to a client that supports them
So do u mean like keep the nas as it is and keep the footage on there etc but get an apple tv device or a nvidia shield?
If so how would the 4k streaming work
Which app would the apple tv connect to be able to view the 4k videos on the nas?