SOLVED: Weird pixelation and stuttering issues when playing on Samsung TV app

[TheDreadPirate]

In the ffmpeg log you provided, for S01E04, there is this block of text.

Code:

Stream mapping:
  Stream #0:0 (hevc) -> setparams:default
  Stream #0:2 (pgssub) -> scale:default
  overlay_qsv:default -> Stream #0:0 (h264_qsv)
  Stream #0:1 -> #0:1 (copy)

If the client was direct playing the subtitles, the pgssub and overlay_qsv lines wouldn't exist.

So it seems that the TV's rendering of SRT subs (SUBRIP) is bunked. Which the TV would be direct playing. Do you have any themes applied to Jellyfin? Did you make any changes to the subtitle rendering settings in Jellyfin?

Settings > Subtitles. The section in the bottom half about adjusting subtitle size and appear.