I’m pretty sure it’s some form of MFSK. It has a definite sync tone and most of the tones are in one part of the passband, which would be the case if it’s only using one part of the character set, similar to how in ASCII, all the letters are in the same part of the set (65-90 for uppercase, 97-122 for lower). It’s definitely a set of discrete tones, as seen in the spectrum waterfall display here:
That’s quite similar to the JT6M waterfall here: JT6M - Signal Identification Wiki
I’ve probably spent way too much time trying to figure this out for someone who has little knowledge of digital encoding though.
ETA: Looks like I was right. It is 128 tone MFSK sending ASCII. The low tones are spaces and higher tones are alphabet characters. Text is the start of the Wikipedia articles for the topic in the description. Some fellow hams on Reddit have figured that out: https://www.reddit.com/r/amateurradio/comments/mxf34z/what_is_this_mode/
Still doesn’t make any sense why the videos exist, though!
