27 bauds! 8-)

Encoding each second:

• audio PPS sync pulse (synchronization accurate to 2 or 3 samples at 48kHz , ie ±60 µs relative to GPS signal)
• SS:MM:HH:DD and version number (2 bits)

Next steps:

1. (naive?) BFSK demodulation on the desktop;
2. time stamping containers  with ffmpeg-python

My tests (with ffmpeg -timecode) show that those containers DO store time stamp metadata: mxf, mov, avi, wmv, mp4 and mkv.

Any NLE has a "position clip in the timeline using metadata time stamp" command or I'll have to fork #kdenlive?  8-)