This absolutely fascinates me. I had a friend who needed subtitle files generating for audio and using in CapCut yesterday yet none of the available stuff was suitable, so he asked if I could adapt some of my software to export subtitles.
2 hours later he's got a fully working piece of local software that does exactly what he wants, yet yours is not able to even sort dates correctly. Feel free to download it if you want to see for yourself, I didn't even do any UI tweaks as this was just a tool for him to use:
Linux - https://downloads.blazingbanana.com/whistle-subtitles/unstab...
Windows - https://downloads.blazingbanana.com/whistle-subtitles/unstab...
Mac - https://downloads.blazingbanana.com/whistle-subtitles/unstab...
How can there be such a massive gap in what can be produced?