HW Transcoding for Windows Clients failing

Plex Media Server Desktops & Laptops
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Server Version#: 1.40.2.8351
Player Version#: 4.125.1

I have a plex server running in a docker container within an Ubuntu 22.04.4 VM Proxmox 8.1.10.

Docker is version 26.0.1, Ubuntu kernel is 5.15.0-102-generic, and Proxmox Kernel is 6.5.13-5-pve.

I have a GTX1660Ti card which I’m splitting across two VMs using vGPU with modified nVidia drivers 535.161.05 using the instructions at PolloLoco / NVIDIA vGPU Guide · GitLab.

HW transcoding has been working, however I’ve noticed in the last week that it’s started failing for Windows clients both in the brower and app.

If I start a 4K HVEC video file, it will start HW transcoding down to 1080p and play okay. However, if I attempt to limit the bitrate (for example down to 4Mbps) it will fail. This also happens when I start a 1080p H264 file, it will play normally and then fail if I attemp to limit the bitrate.

Weird thing is, that if I turn subtitles on and then limit the bitrate, it will work for 1080P H264 files but not not 4K HVEC.

Monitoring the GPU processes in the VM using the command watch -n 0.2 nvidia-smi I can see that Plex is attempting to start a transcoding process multiple times but appears to fail. It does the same thing when starting a 4K HVEC file or with subtitles but eventually starts working.

If I use the Plex Android app on my phone I can adjust the bitrate without issue.

I’ve also spun up another Ubuntu 22.04.4 VM and installed Plex using the deb file, rather than in a Docker container, and it also has the same issue.

plex-HVEC-HWTranscode.log (680.2 KB) - 4K HVEC on Windows
plex-H264-HWTranscode.log (363.4 KB) - 1080P H264 on Windows
plex-HVEC-HWTranscode Phone.log (151.6 KB) - 1080P H264 on Android Mobile

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Tried a split passthrough of the iGPU for my i7-7700K to the Ubuntu VM and Plex Docker container and selected the HD630 over the GTX1660Ti. HW transcoding for Windows cilents worked flawlessly, with playback restarting almost straight away when I lowered the bitrate limit.

plex-H264-HWTranscode-iGPU.log (209.3 KB)

Appears to be an issue with the GTX1660Ti. Anyone encountered similar issues?

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Did you do any updates recently? Seems there is plenty of hw transcoding issues going on atm after updates.

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I’ve tried downgrading Plex back to 1.32.8 but it still has the same issue. My next step is to play around with the nVidia driver versions.

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After playing around with different combinations of kernel versions both for Proxmox and Ubuntu, nVidia driver versions, and Plex versions I’ve identified that the issue arises when I’m using vGPU to split my GTX1660 Ti across multiple VMs. It doesn’t matter whether it’s inside or outside of a Docker container.

If the GPU has a dedicated passthrough to the VM running Plex then HW transcoding works okay for Windows clients regardless of which nVidia drivers I use.

I’m not sure whether this is a driver issue, a Plex issue, or a combination of both.

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