Hi all, so I bought 4k HDR monitor for my PC and I wanted to stream some HDR content from my plex server. When I first fired it up and played some HDR content via Plex HTPC it worked perfectly fine, with almost 0 CPU load on my server fast scrubbing on the timeline, etc. After that, I turned off my PC as well as my plex server just to come back a few hours later and find out that for no reason plex is transcoding my HDR content to SDR. It’s transcoding HEVEC 4k HDR to H264 4k SDR 
I installed also Plex player to check if there is any difference but nope, it’s still transcoding my stuff to SDR. I have HDR enabled in Windows (checked that a few times) and I’m running out of ideas. Does someone know how to forbid plex to transcode HDR stuff?
When you went away, did you turn off the computer or walked away and left it running? If the latter, did the monitors go to sleep? It’s possible when they woke up, the hdmi handshake with your computer didn’t work well so your computer doesn’t know they are HDR capable. Try turning the monitor off and back on to re-establish the hdmi handshake. If that doesn’t work, you can try restarting your computer. Could be something with the graphics card that flaked out.
When I left I turned off both my PC and monitor as well as my plex linux server. I already tried restarting PC as well as the monitor but without any luck. I’m using displayport with DSC (without DSC same problem).
Some additional info regarding Windows, HDR, & Plex HTPC:
It was working so I don’t know why I should suddenly do this in order to make it work again but ok I tried I followed the instruction replaced dll file created conf file, disabled hdr switching and nothing changed, same problem
Ok looks like the server-side is broken because my iphone 12 pro was able to stream 4k hdr even before I bought the monitor and now even for the iPhone app it’s converting movies to SDR. Do you know what kind of settings can “force” such behavior?
Just a thought. Have you tried to disable HDR in Windows? Then play something with HDR in Plex HTPC.
Because I don’t have HDR enabled.
Plex HTPC automatically enables it. But I think it only sends instructions to the TV to enable HDR mode.
Anyway, my thoughts was that perhaps Plex HTPC only toggles HDR. Meningen not actually checking if it’s on or not. So instead of enabling HDR on Windows it turns it off (because it was already on) 
HDR enabled/disabled in Windows has no effect on whether the server will transcode or not. Usually a client getting a transcode when it wasn’t before is due to the connection method. Likely your client is connecting to the server over the WAN or proxy connections instead of the LAN. You should check this.
Okey, I tell you due we have a problem. When I booted my PC today HDR was ENABLED! So Plex is messing around.
Ok, so I disabled remote access to avoid going through WAN (even tho I have 1Gb/s upload so I should be able to push max quality), but even that didn’t help, however, I started messing around with the network so my plex server is in a different local subnet than my computer and phone, and suddenly when I moved my computer to the same subnet I have no more transcoding and it plays 4k hdr on my screen. Can someone explain to me why plex sees other LOCAL subnets as WAN network? And how to change it? I’m not blocking any traffic between these subnets (ofc. subnets them selves are blocking broadcast but that’s it).
Plex Documentation → Server Settings → Network
Settings → Network → LAN Networks
Comma separated list of IP addresses or IP/netmask entries for networks that will be considered to be on the local network when enforcing bandwidth restrictions. If set, all other IP addresses will be considered to be on the external network and will be subject to external network bandwidth restrictions. If left blank, only the server’s subnet is considered to be on the local network.
Example: 192.168.1.0/24,10.1.2.0/24
Example: 192.168.0.0/16
Note 1: No space after the comma between subnets.
Note 2: A Plex Pass is required.
You can monitor Settings → Console or the server logs:
Console output when entering 192.168.0.0/16:
Request: [192.168.1.55:60251 (Subnet)] PUT /:/prefs?LanNetworksBandwidth=192.168.0.0%2F16 (11 live) TLS GZIP Signed-in Token (FordGuy61) (Chrome)
Completed: [192.168.1.55:60251] 200 PUT /:/prefs?LanNetworksBandwidth=192.168.0.0%2F16 (11 live) TLS GZIP 1ms 320 bytes (pipelined: 1)
You’ll see an error message if the information is entered incorrectly.
Console output for 192.168.1.0/24, 192.168.2.0/24 (illegal space between subnets)
Request: [192.168.1.55:56850 (Subnet)] PUT /:/prefs?LanNetworksBandwidth=192.168.1.0%2F24%2C%20192.168.2.0%2F24 (10 live) TLS GZIP Signed-in Token (FordGuy61) (Chrome)
Error parsing allowedNetworks ' 192.168.2.0 24': Invalid argument
Completed: [192.168.1.55:56850] 200 PUT /:/prefs?LanNetworksBandwidth=192.168.1.0%2F24%2C%20192.168.2.0%2F24 (10 live) TLS GZIP 1ms 320 bytes (pipelined: 1)
LAN Networks
Very few people will need to set or change this preference. It simply lets you specify which IP addresses or networks will be considered to be “local” to you. If you set any bandwidth limits under Remote Access, those do not apply to “local” playback and only take effect for remote playback. By default, only the network subnet on which the server is located is considered to be “local” (which is appropriate for the vast majority of users).
Tip! : This feature requires an active Plex Pass subscription for the Plex Media Server admin Plex account. Addresses can be specified either as an individual IP address or a range (using IP/netmasks). Do not include spaces or tabs.
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