I beg to differ, I have one Roku Ultra 4k that does play HEVC, but the 2 older 4460x Roku Ultra 4k cannot play HEVC, as I said, it took almost 2 hours with Roku tech to find this out. The older Roku's are advertised as being able to play 4k, but it may be limited to HDR10 4k, I am not sure.
SFBaysailor
You are confusing codecs with Dynamic Range.
HEVC is a Codec and HDR10 is the Dynamic Range.
HEVC/H265 is used for 4K content because the compression is way better than AVC/H264. A full 4K movie in H264 could be like 100 GB instead of 30 GB with H265.
I really doubt that the Roku supports H264 HDR10 as there probably isn't any hardware that supports 10-bit H264 aside from maybe professional equipment. The bitrates needed to encode 2160p H264 HDR10 would be insane.
If anything, it may support 4k H264 at Level 5.1 but absolutely not with HDR10. I still don't understand the logic of using H264 for 4K though...