It depends on the nature of watched stream. If it’s DRM L1 protected (like Netflix streams) it will be always decoded via “Input Stream” and that is software decoding. No way to get HW decoding in that case.
If the stream is L3 protected (like HBO_Go streams) then it will be decoded via players HW decoder.
Btw, S912 has not enough juice to software decode 1080p DRM L1 (it can do 1080p L3 ones) protected streams, let alone 4k streams…