Plex Transcoding Issue - HEVC Main 10 HDR 4k Movies

General Discussions
1

Hey Guys,

I am having some issues with hardware transcoding HEVC Main 10 HDR 4k movies. Here is my current setup.

CPU: Intel i7 4930K
GPU: Nvidia GTX 1070
RAM: 32GB
OS: Windows 10 PRO

What I have found in my testing is, when I transcode 4K HEVC Main 10 HDR movies down to 1080p. it does transcode but the playback is not smooth. (It plays for a second or two and buffers for a one/two seconds and it process continues). The resource usage on my computer is CPU around 40% and GPU is less than 9%. Playback at 720p 4Mbps works fine with CPU usage around 30% and GPU around 13%.

If I transcode non HDR 4K movies (H.264 or even HEVC Main 10) to 1080p. Works fine with CPU at around 18% and and GPU around 24%. Infect I can play 3 streams at a time without any issues.

Based on this testing, I feel that the HDR movies are not being transcoded by GPU. Is this a limitation of GTX 1070?
Has anyone faced such issue, Will it fix my issue if I upgrade GPU to something like Nvidia Quadro P2000 or P2200 ?

Thanks.

2

Plex Media Server version?

Turn off HDR tonemapping in Settings → Transcoder (show advanced if needed). Tonemapping is not supported on Nvidia w/ Windows, so it will hit your CPU instead.

To see if your GPU is in use for transcoding:

  • Using Plex Web, go to Settings → Console
  • Filter for TPU:
  • Play a movie. Force a transcode if needed.
  • You should see NVDEC/NVENC for the decoder/encoder if Plex is transcoding with the 1070.

Additional Information:
Using Hardware-Accelerated Transcoding
HDR to SDR Tone Mapping

Sample Output:

Screenshot (504)
Screenshot (504)1402×227 69.4 KB

3

Thanks. Turn off HDR tonemapping worked. However, The HDR movies looked washed out after transcoding. But I guess that is what expected without tone mapping. I found the post in another forum that confirms the tone mapping is not supported in Windows using Nvidia GPU. However, it is supported via software.

So I temporarily installed Plex Server on my main working PC.
CPU: Ryzen 3950x
GPU: RTX 2060

The transcode of HDR content with Tonemapping enabled worked just fine on this computer. I guess the this CPU is capable enough to software transcode HDR content.

So another question here: Which would be the most cost effective CPU (New or old) that will easily transcode HDR content. I definitely can’t afford another 3950x for Plex server.

4

Why are you transcoding a 4K movie in the first place? Why not just create an optimized version of it 1080p for non 4K TVs or for remote streaming.

5

Maybe someone from Plex or someone who has been testing on Linux can provide more info.

I run Plex on a Synology NAS w/ a Celeron CPU. Even with hardware acceleration, transcoding 4K is limited. Tonemapping is out of the question. Hardware accelerated tonemapping is not available yet for PMS on Synology and the CPU is no where near powerful enough to handle it.

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