Hey guys. I currently have an Intel i5 8400 that does its job quite well. Two of my clients are webOS, which regularly leads to transcoding (DTS etc, you know the drill). As soon as subtitles are in the game (SRT), HW transcoding is no longer possible, so the CPU has to fight alone. For 4K>1080p with tone mapping, the 8400 is too weak (speed 0.8).
Which CPU would be able to do the conversion on the fly? Does anyone have experience?
(Ubuntu x64)
That’s a weak processor for transcoding.
Do you have Burn Subtitles set to AUTOMATIC?
SRT subs which are always process on the CPU shouldn’t be bumping you out of HW transcoding.
To answer your question, for 2 CPU transcodes of HDR media you are looking at something around an i7-12700. Not sure if the hardware HDR drivers for the 12th gen are 100% yet.
Yes, it is. WebOS forces a video transcode with burning subtitles when audio needs to be converted and subs are enabled (whether SRT or PGS doesn’t matter). According to the Plex team, this is required for synchronicity. A massive limitation von LG devices, unfortunately.
I only need 1x 4k-to-1080p transcode, because tone mapping in conjunction with subtitle burning isnt multi-core compabitle. If a CPU has enough power to run the process with primarily one core, more should not be a problem.
There are no tables from developers here that show which CPU is required for this. I need experience reports. 
If you have a FCLGA1151-2 socketed motherboard you can drop an i9-9900K to get you to the PassMark recommended by Plex.
When burning subtitles the video is still transcoded using the GPU. The limitation is that combining the video and the subtitles frame by frame is performed on the CPU and is single threaded.
I’ve a Lenovo ThinkCentre with an i5-10500T. It struggles with transcoding/tonemapping 4K HDR and burning subtitles. This is expected, as its single core Passmark rating is similar to your i5-8400.
Like you, I’ve not seen a good reference for what single core rating is necessary to burn subtitles when transcoding and tonemapping.
PassMark has a list of CPUs sorted by single core scores: PassMark Single Thread Performance.
Alder Lake support for Linux will be in the 5.18 kernel later this year. I do not know if/when it will be available in Ubuntu 20.04 or if it is destined only for the 22.xx LTS release.
Intel’s Thread Director Coming to Linux 5.18 to Fix Alder Lake Performance Issues
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