Transcription of video and audio calls for the deaf and hard-of-hearing

To allow participation by deaf and hard-of-hearing on live video calls. :hear_no_evil:
All ideas and suggestions for how to accomplish this appreciated. See the links for details on each Github feature request. Thanks!

Wiki post. Please edit me with suggestions. Open, permissive licenses are obviously the preference, but keep in mind those without hearing must use whatever is available.