HW Transcoding with HDR Tone mapping not working (hw works without tone mapping enabled)

Plex Media Server
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Server Version#: 1.25.8.5663
Player Version#: 4.69.1 (web player)
Unraid Version: 6.9.2 2021-04-07 (docker repo is set with :plexpass)
CPU: I5-11400

It took me way to long to figure out the reason my HW transcoding wouldn’t play videos on my 4K HDR files was because of this HDR Tone Mapping setting. As far as I can tell, everything in my hardware is supposed to support this feature. But, if I have HDR Tone Mapping enabled and start playing a 4K HDR file that needs to be transcoded, it will just spin for a minute or so and never actually play the video. If I watch the Intel GPU top graph, Render/3D will max out during this time and then everything will just go to 0% usage.

I’ve checked in the logs to see if I could find any errors and I can’t find anything. It just loops through some transcoding tests and then eventually kills off the transcoding session. Never outputs any error.

If I turn off the HDR Tone Mapping the hw transcoding works perfectly. Can anyone tell me why this is? I’m not even sure if I really care about this setting, the picture looks fine to me without it, but if it’s supposed to improve the picture quality of transcoded HDR content, I’d like to see if it does in fact look better.

Thanks

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THANKS!! I used way too much time to solve that problem too. Thank you for posting!

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So… is this a bug, or is there some configuration issue preventing this from working for me?

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I think the issue is related to tone mapping being CPU bound. Even on my main (not the server) rig with a 5900x and 3080 it cannot do 4k->2K HDR /w tone mapping enabled. The CPU load goes very high and hits the spinner constantly. I just disabled tone mapping.

When tone mapping is used, I suspect the transocoder is using the ffmpeg scale filter to scale HDR->SDR and that’s 100% on the CPU. So you have compressed media going to the GPU, getting decoded, getting pulled into system memory, tone-mapped, then pushed back to the GPU to be encoded. Maybe I’m wrong.

If anyone has 4k->2K HDR /w tone mapping working well please share your system specs. I cannot get it working on a 5900X /w 32GB and a 3080.

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