SOLVED: Problems with TRANSCODING (TrueNAS)

[TheDreadPirate]

By default ffmpeg will always transcoding as fast as possible all the way to the end of the file. You can enable transcoding throttling in Jellyfin. This will cause ffmpeg to pause when the transcode gets a few minutes ahead of the current playback position.

Direct subtitle rendering varies per client. The videos you've shared all have PGS subs. Direct PGS rendering is only supported on jellyfin-web, at the moment. And that is still experimental.

https://forum.jellyfin.org/t-native-pgs-support

SRT subs can be directly rendered on pretty much all clients. ASS subs are supported in Jellyfin-web on most browsers and partial, unstyled, support in Android when using exoplayer. DVD/VOBSUB subtitles are always burned in.

Audio passthrough also varies by device. If the device manufacturer paid for the license to do audio passthrough, Jellyfin should be able to do that if you enable it.