I have built my own local-first solution to transcribe entirely locally in real time word by word, driven by a different need (I'm hard of hearing). It's my daily driver for transcribing meetings, interviews, etc. Because of its local-first capability, I do not have to worry about privacy concerns when transcribing meetings at work as all data stays on my machine. It's about as fast as Otter.ai although there's definitely room for improvements in terms of UX and speed. Caveat is that it only works on MacBooks with Apple silicon. Happy to chat over email (see my HN profile).
I have some staff with combined hearing and visual needs. Have you researched the one-, two- all-party consent requirements? Asking because I hope to identify transcription as "non-recording".
California has an exception for hearing aids and other similar devices, but it’s unclear if transcription aids count, or if this has been tested in court. https://codes.findlaw.com/ca/penal-code/pen-sect-632/ (Not a lawyer, this is not legal advice.)
Do you mean ephemeral, or are you actually wondering about something implanted under the skin? I'd think/hope if it goes under the skin, it ends up in "hearing aid" territory. I'm less sure about if it doesn't persist.
Two/all-party consent are hacky workarounds for the actual harm being inflicted (valid goals including not having your microwave inform Google's ad servers, not recording out-of-context jokes as evidence to imprison people, ... -- invalid goals caught up in the collateral damage include topics like the current one about hearing issues (note that a sufficiently accurate transcription service has all the same privacy problems 2-party consent tries to protect against, maybe more since it's more easily searchable)).
I'd be in favor of some startup pulling an Uber or AirBnB and blatantly violating those laws to the benefit of the deaf or elderly if it meant we could get something better on the books.