[anthonj]

That's considered a feature in the community. Burning subs on the video trace is considered bad, but most video player will not automatically show any subtitle track.

[AgentME]

Are there standards for a video to declare a default subtitle track to use?

[anthonj]

Oh looks like there is. mkv does and looks like mpv and vlc will respect that flag. For other formats I'm not so sure