Windows server unable to transcode 4k HDR to 1080p SDR--but the hardware should be up to it?

Plex Media Server Desktops & Laptops
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Server Version#: Windows 1.24.0.4930
Player Version#: Windows 1.33.0.2444-a220eae4

I’m trying to play a 4k file with transcoding down to 1080p for tone mapping. Tautulli tells me the transcode speed is 0.9 to 1.2. It is usually between 0.9 and 1.0, so I do get frequent buffering pauses making the video unwatchable. My question is… why?

File stats

Video: 57 Mbps 4k HEVC Main 10 HDR, 24 fps (MKV)
Audio: DTS-HD Master Audio / 7.1 3835 kbps

Server info

  • The server is an Intel 10700k with a GTX 1070 (Windows 10, current Plex server, Plex pass for hardware support.)
  • The server is idle other than PMS dishing up this one stream and this has been a very well behaved Windows gaming box so far.
  • Every device is on a gigabit hardwired LAN which I have no reason to believe is faulty. (I can direct play high bitrate files with no problems.)
  • PMS is configured to use hardware acceleration
  • GPU-Z tells me the server GPU load is about 6% during transcoding. (It does bounce around between 3-7%.)
  • The Windows Plex Transcode executable is at about 30% CPU.

Should I expect a high bitrate 4k HEVC HDR file to be unwatchable with this server, or should I expect better performance? If I should be seeing better performance… where do I start?

(I did try another 4k HDR file with a total bitrate of about 19 Mbps. This file can be played succefully at 1080p, with a reported transcode speed of 1.0 - 1.5. Is that low, or expected?)

Thanks if you have any ideas for me!

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Plex can’t utilize your GPU for HDR to SDR transcoding. That’s likely your issue here. Tone-mapping is extremely resource intensive, even for a beefy CPU.

1 Like
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Thanks much. Somehow I missed that, that article is just what I needed.

Interesting that CPU hardware support is only partial under Windows, and there’s no GPU support at all… Linux has it all, but FreeBSD has no hardware support at all. :man_shrugging:

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