/u/DaveBinM Wow thank you so much. I've tested this with 80+ movies and (almost) all of them hardware transcode and hardware tone map. The only one that doesn't is GOODFELLAS. It only works via software transcode and software tone map which maxes out my CPU. I have an Intel NUC 8 i5 with Ubuntu 20.04.1. I'm running Plex Server 1.21.0.3616-d87012962.
Here's a dump from mediainfo, if this is any use. And comparison with a movie that play fine. Both examples are HEVC Main 10 HDR. Neither of these movies have subtitles.
GOODFELLAS
Unique ID : 118521303854905584085425973103478115205 (0x592A5F70C05452434FFBE18A26E30B85)
Complete name : /Volumes/Media/Video/Movies/Goodfellas (1990)/Goodfellas (1990).mkv
Format : Matroska
Format version : Version 2
File size : 80.4 GiB
Duration : 2 h 25 min
Overall bit rate mode : Variable
Overall bit rate : 79.2 Mb/s
Movie name : Goodfellas (1990)
Encoded date : UTC 2019-12-13 22:15:14
Writing application : MakeMKV v1.14.7 win(x64-release)
Writing library : libmakemkv v1.14.7 (1.3.5/1.4.7) win(x64-release)
Video
ID : 1
ID in the original source medium : 4113 (0x1011)
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main [email protected]@High
HDR format : SMPTE ST 2086, HDR10 compatible
Codec ID : V_MPEGH/ISO/HEVC
Duration : 2 h 25 min
Bit rate : 74.8 Mb/s
Width : 3 840 pixels
Height : 2 160 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0 (Type 2)
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.376
Stream size : 75.9 GiB (94%)
Language : English
Default : No
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0050 cd/m2, max: 4000 cd/m2
Maximum Content Light Level : 500 cd/m2
Maximum Frame-Average Light Level : 200 cd/m2
Original source medium : Blu-ray
For comparison, here's a movie that hardware transcodes and tone maps just fine…
HOT FUZZ
Unique ID : 226905922002886112962860664724805483670 (0xAAB47DB07FD0DAEAE564A6B7CA857C96)
Complete name : /Volumes/Media/Video/Movies/Hot Fuzz (2007)/Hot Fuzz (2007).mkv
Format : Matroska
Format version : Version 2
File size : 51.9 GiB
Duration : 2 h 0 min
Overall bit rate mode : Variable
Overall bit rate : 61.5 Mb/s
Movie name : Hot Fuzz
Encoded date : UTC 2019-12-11 08:22:50
Writing application : MakeMKV v1.14.7 win(x64-release)
Writing library : libmakemkv v1.14.7 (1.3.5/1.4.7) win(x64-release)
Video
ID : 1
ID in the original source medium : 4113 (0x1011)
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main [email protected]@High
HDR format : SMPTE ST 2094 App 4, Version 1, HDR10+ Profile B compatible
Codec ID : V_MPEGH/ISO/HEVC
Duration : 2 h 0 min
Bit rate : 52.6 Mb/s
Width : 3 840 pixels
Height : 2 160 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 23.976 (24000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0 (Type 2)
Bit depth : 10 bits
Bits/(Pixel*Frame) : 0.265
Stream size : 44.4 GiB (85%)
Writing library : ATEME Titan File 3.9.0 (4.9.0.0)
Language : English
Default : No
Forced : No
Color range : Limited
Color primaries : BT.2020
Transfer characteristics : PQ
Matrix coefficients : BT.2020 non-constant
Mastering display color primaries : Display P3
Mastering display luminance : min: 0.0050 cd/m2, max: 1000 cd/m2
Maximum Content Light Level : 960 cd/m2
Maximum Frame-Average Light Level : 336 cd/m2
Original source medium : Blu-ray