Default SRT subtitles

[ZoMbIe828]

How do I make SRT subtitles come on as default? When I open a video file in AVIMux_GUI or MKVToolNix, the subtitle says that it's already default. I tried turning it off default, muxing it and turning it back on as default, but it still doesn't appear as default when you play it.
How do I make SRT subtitles default upon playing?

[Skelsgard]

The player is the one that supports or not embedded subtitles and/or ON by default.

Cheers.