From what I remember, some clients don't support streaming subtitles, so they must download them completely in advance, when the movie starts, before they start appearing. If you pick embedded subtitles with these clients, Jellyfin must extract the subtitles files immediately, and this takes a while depending on container format, file sizes and server load. External subtitles are faster.
I personally use Bazarr instead, because I also want to download subtitles for different languages. In Bazarr, Embedded Subtitles is just another subtitle provider that can fetch subtitles depending on your rules.
Really? How?
My expectation would be that extracting a subtitle file takes a few seconds at most. If you had to do it on the fly every time you watched anything in your library, it wouldn't matter.
ffmpeg -i input.mkv -map 0:s:0 /tmp/subtitles.srt
I also remember Google TV working fine, but it seemed like ads got added to another part of the UI every month so I got sick of it.
Roku only supports text subtitles, so if you have picture subtitles (like a DVD or bluray), then you'll need to burn them in if you want to play on Roku.
Young children and non technical adults can use it as easily as any streaming app. I guess you can tweak and theme it endlessly to look like your favourite streaming app but I haven’t felt the need to so far.
Self-hosting always involves a bit of jankiness, if you can’t handle that then back to overpriced subscriptions and spyware you go.