oh there are HUGE differences in "hard of hearing/hearing impaired" and usual subtitles:
just some examples - good subtitles for "hearing impaired" contain:
- a hyphen ("-") when speaker changes (otherwise a deaf person won't recognize the change)
- "non dialog audio descriptions" like [Shot fired] or [Telephone rings] (those are extremely important as they are changing the storyline - e.g. a person shots himself while not being seen
- italic font for showing that the person is not seen or he/she is singing
-
"Onomatopoeia" - sometimes there appears text like <Beep, beep> e.g. for R2D2
- Color! German television broadcasts with colored subtitles - I usually upload colored and non-colored subtitles (color is way better for distinguishing the actor - e.g. when it is a voice-over)
- Position - sometimes subtitles are placed where the speaker is being seen OR where the sound appears to come from
- Music is transcribed like "♪ Sweet Home California ♪"
So it is crucial to have both: subs for hard of hearing AND just usual subtitles (because some people are annoyed by lines like [computer beeps].
It would be perfect if you are able to support colored subtitles - be aware that they are usually in different formats (typically ASS/SSA).
If you have any questions about formats and timings, don't hesitate asking me.