Ugly image in 4K while 1080p trancoded is ok

Plex Players
1

Server Version#: 1.42.2.10156-f737b826c
Player Version#: 10.30.8.4222 Android (both on Shield TV Pro and TCL Android TV)

Plex Server is a remote MacMini 2018 with integrated GPU (used for HW transcoding).
Plex players are a Shield TV (plugged into a Samsung TV) and a TCL TV.
Same issue with both players, both TV are 4K and HDR compliant (all “image enhancers” are disabled on TV).

I wanted to a watch an episode (tried on all episodes of two different TV shows) that is H265 4K HEVC-10 encoded:
Codec HEVC
Bitrate 18717 kbps
Bit Depth 10
Chroma Location left
Chroma Subsampling 4:2:0
Coded Height 2160
Coded Width 3840
Color Primaries bt709
Color Range tv
Color Space bt709
Color Trc bt709
Frame Rate 25 fps
Height 2160
Niveau 5.1
Profil main 10
Ref Frames 1
Width 3840
Display Title 4K (HEVC Main 10)
Extended Display Title 4K (HEVC Main 10)

It doesn’t look like a a bandwidth issue between server and client, no stuttering at all.
Plex client estimated the bandwidth need to 18.4 Mbps (original format) with 70+ Mbps available between client and server (speedtested).

But the image is ugly: not smooth, grainy, lots of noise (in french I would say “ça fourmille”), burnt whites.

If I get the server to HW-transcode it (to the best 1080p choice available), image is much better (no more grain/noise).

Watching a x265 4K HDR movie with following specs is OK.

Codec HEVC
Bitrate 6592 kbps
D O V I B L Compat I D 1
D O V I B L Present true
D O V I Level 6
D O V I Present true
D O V I Profile 8
D O V I R P U Present true
D O V I Version 1.0
Bit Depth 10
Chroma Location topleft
Chroma Subsampling 4:2:0
Coded Height 1632
Coded Width 3840
Color Primaries bt2020
Color Range tv
Color Space bt2020nc
Color Trc smpte2084
Frame Rate 24 fps
Height 1632
Niveau 5.1
Profil main 10
Ref Frames 1
Width 3840
Display Title 4K DoVi/HDR10 (HEVC Main 10)
Extended Display Title 4K DoVi/HDR10 (HEVC Main 10)

Any idea what could cause this and how to this it?

2

The first video doesn’t contain any HDR information. And its color space is bt709, which is the regular color space for full HD television devices. In other words, its colors are in standard dynamic range (SDR).
It’s rare to find 4K resolution videos with just standard dynamic range (SDR), instead of HDR.
Unless it was simply upscaled from FHD to 4K, I assume it was originally in 4K and HDR, and then something must have gone wrong while it was encoded.

On the other hand, the “working” video has proper HDR color. Both the color space definition of bt2020nc and the DolbyVision and HDR10 data are present. So color representation is accurate when played back,

3

I just checked the nfo and it was actually released as “4K H265 10 bits SDR” (source: webDL).
Just like you said… Guess it’s a broken upscale of encoding.

I’ll try to fetch a 1080p release and compare.

Thank you.