Performance issue with subtitles

[ElFeo]

So I just updated to the latest version of jellyfin - running on a Rpi 5. I hade no performance issues running movies/series including subs before the upgrade but now enabling subs makes the CPU go from 5-30% up to 100%. Setting subs to off and the CPU goes down to 5-30%. Are there any settings around subs I can try?

[TheDreadPirate]

What kind of subs and on which type of client?

[ElFeo]

Its the web client. The subs are "included" in the mkv-file (or is there some pluging to jellyfin finding subs?)

Edit: The client is a Macbook but the performance issue is on the Rpi 5 server

Edit2:
Server version 10.10.7
Web version 10.10.7
Build version 10.10.7

[TheDreadPirate]

But are the subs SRT subs or ASS? PGS?

Can you share your jellyfin log via privatebin.net?

[ElFeo]

The subs are "embedded" in the mkv file. So not sure what they are, it's not a separate file.
Which logs are you looking for? Seems like its one per day and then a bunch called FFmpeg in the beginning.

[TheDreadPirate]

log_20250411.log and any one of the logs named FFmpeg.Transcode at the beginning.

[ElFeo]

https://privatebin.net/?a0d809c9c4893b77...kocQDF1ebD
https://privatebin.net/?d27f79c710265991...L4ULqxL2B1

[TheDreadPirate]

They are PGS subs and they are being burned in, which requires transcoding. And the transcoding is being done on the CPU.

Code:

Stream mapping:
  Stream #0:0 (h264) -> setparams:default (graph 0)
  Stream #0:2 (pgssub) -> scale:default (graph 0)
  overlay:default (graph 0) -> Stream #0:0 (libx264)
  Stream #0:1 -> #0:1 (dts (dca) -> aac (libfdk_aac))

There is an experimental setting in jellyfin-web to direct play PGS subs. Settings > Subtitles. Check "Experimental PGS subtitle rendering". From my experience with direct PGS rendering in a browser, the subs will sometimes de-sync briefly.

Your other option is to use Jellyfin Media Player, which has a much better playback engine.

[ElFeo]

Ok, thanks for figuring stuff out! Ill try the setting...

[ElFeo]

Interesting, just tried the client for Mac and that gives me the same amount of CPU-% as without subs. Maybe a bug in the web-client?