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+--- Thread: 4k activating subtitles causing high CPU and GPU usage (/t-4k-activating-subtitles-causing-high-cpu-and-gpu-usage)
4k activating subtitles causing high CPU and GPU usage - zzz00 - 2025-03-28
Recently set up Jellyfin and have trouble with 4k HDR content. Using Jellyfin media player, playing a 4k HDR movie on a 4k (technically HDR) monitor using HDR mode, I see ~15% cpu usage, 0% gpu. Activating subtitles brings it all the way up to ~70% cpu and 90% gpu usage. I also get some stuttering and if I go forward or back, I have a ~30 second delay before video plays. Have the same issue on my iPad, haven't even tried my TV yet but that's the ultimate goal here. Is this normal or am I missing something here?
I was hoping to be able to have 2 simultaneous 4k streams on my system. I have a 4070 ti super and activated hardware transcoding NVENC (literally all the options), and most everything is in defaults except transcoding all checked off. Subtitle extraction on the fly is on and I tried turning on throttle transcodes to see if it helped but it doesn't seem to.
Should I also turn on Delete Segments? I seem to already have 50gb in the transcoding folder after just testing to see if changing settings fixes the subtitles issue
Using windows installed, 10.10.6
RE: 4k activating subtitles causing high CPU and GPU usage - TheDreadPirate - 2025-03-28
"Throttle transcodes" does not slow down ffmpeg but it will pause it once it gets ### seconds ahead of the current playback position (configurable). Same with delete segments. Deletes transcode segments ### seconds after you've passed them.
Jellyfin Media Player does not truly support HDR, btw. Due to limitations in some of the libraries used to build it, HDR is not possible. But a re-write is currently in the works.
In the mean time, Jellyfin MPV Shim does support HDR rendering, but requires modification to do so. Read this thread.
https://forum.jellyfin.org/t-how-can-i-enable-hdr-playback-in-windows
As for the CPU/GPU usage, I'm assuming it is transcoding. Not sure why it would since JMP should direct play nearly everything. Unless you've configured subtitles to always be burned in.
RE: 4k activating subtitles causing high CPU and GPU usage - zzz00 - 2025-03-28
Thanks for the response. Gonna look at MPV Shim.
Burn Subtitles setting is at auto. Subtitles in the one I'm testing is BD PGS subtitles (bdpg). Looks like that one is always burned in. Going to try the experimental PGS rendering and see how that works. So far it helps for JMP on PC only, not ipad. Do you happen to know what the smart subtitles setting is? Couldn't find any documentation
RE: 4k activating subtitles causing high CPU and GPU usage - TheDreadPirate - 2025-03-28
I don't know what the decision logic is, but my understanding is that it will use a mix of your language preferences in combination with what audio language is the "default" in the video you are playing.