One obvious optimization is to sample the audio file at regular intervals and transcribe only a part of the text. Then just interpolate the locations. This can speed it up by a couple of orders of magnitude.
And I haven't realized that you can actually see sentences highlighted as they are being read. I'd love that for Chinese (I'm learning it, so it'd help me a lot). I'll try and see if it "just works", and contribute a patch if it doesn't.
Simplified Mandarin: https://youtube.com/playlist?list=PLVlVz7EDz7fprPeVpqQCvlkMI...
Traditional Mandarin: https://youtube.com/playlist?list=PLVlVz7EDz7fpQZr29P5hqVveL...
... also 33 other languages https://youtube.com/@literature_for_eyes_and_ears/playlists
I left it to languish once I discovered the demand wasn't that great and I was spending more time making the videos than people ultimately spent watching them.