Add default subtitles to video file

[Litafae]

Often mp4 or other video files will come with built-in (not hardcoded!) subtitle options that the user can toggle.

I have an srt.

I have an mp4.

I can manually load the srt to the mp4 on a single playing instance.

How do I combine the two so that the mp4 will contain the subtitles without a separate srt?

I am not trying to re-encode with burned-in subtitles.

[ProWo]

Use clever Ffmpeg-GUI to mux your srt to the mp4 video.
Load your mp4, click main, click multiplex, drag & drop the srt file into the grid, select mp4 as container and click multiplex.
Done.

[noemi7]

Depends on system, and a player but i.e. most PC players and TV sets display separate subtitles if it filename is the same as the video.

[Litafae]

Brilliant. Mux appreciated.