Yay, finally figured out a way to archive #MythTV recordings, maintaining the 888 CC subtitle stream.
I did discover aged tools before, but that no longer worked. I thought it'd be tricky.
But, I was clearly overthinking it.
Last night cooked together a bunch of scripts that use #CCextractor and #FFmpeg to get an SRT file and a more agressively re-encoded and de-interlaced MP4 stream that I then combine into a single MKV file.
4.7GB in, 970MB out, all without any noticable quality loss. 🥳