Following these naming conventions:

this is my video.mp4

the subtitles are being called:

this is my video.deu.srt

this is my video.eng.srt

and coexist with the source files.

These can be automatically recognized (source directory) and automatically imported to result as soft subtitles, for MP4 this would be Timed Text. For MKV this can stay as SRT.

Burn in, especially for forced subtitles could be an valuable option.

Additionally, it would be very helpful to support auto track naming and language tagging in resulting file:

this is my video.forced.deu.srt - a forced subtitle in german language
this is my video.sdh.deu.srt - subtitle optimized for hearing impaired in german language
this is my video.normal.eng.srt - standard subtitles with no hearing impaired explanations

What do you think about this?