Video Stutterin, is this a transcoding issue?

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Could you please post your log to privatebin.net? Makes it easier to parse. Seems to be transcoding just fine (6x+).

I have tried to enable hardware transcoding for all plugins, but it also didn't help.

Yup. Find your CPU/GPU in the options here: https://jellyfin.org/docs/general/post-i...eleration/

Follow those instructions to ensure your host is set up correctly. I'd recommend uploading the log first so we can take a look.

Also, why are subtitles and audio codecs not supported? Do I need to download it on the server?

No. This is all because of your client (and media). Unless you have a device capable of direct playback of Dolby TrueHD Atmos, the audio will be transcoded. The entire media file is being transcoded because of the subtitles. Bluray subs (PGS - presentation graphic stream) are not supported in direct play with the vast majority of clients. Turn off your subtitles and I'd guess -- if your client is capable of playing 4K HDR -- only the audio will be transcoded.

You should avoid media (or re-encode lossless sources) with codecs you can't play. If you're running a TV with just the internal speakers, you will NOT notice a difference between Dolby TrueHD Atmos and AAC if the bitrate is in the sweet spot. Also avoid PGS, VOB, DVD, complex ASS/SSA, and VTT subs if you want to avoid transcoding.