As a musician, audio engineer, and software engineer, this just blew my mind. I can't believe I've never heard of or thought of this until now. But my primary focus has been non-audio software through the pandemic, so I haven't been actively trying to find solutions to this. Thank you.

What applications would you recommend? Can it also do video, if not each link in the chain, at least one camera for the conductor (the node providing the metronome audio)? I realize the conductor would hear nobody at all, until playing back a recording from the end of the chain. Playback of said recording could begin after the song, or one measure into the song if there are no tempo/time changes (NINJAM style).

There's a sea shanty called the Wellerman that recently blow up on TikTok, and listening to it I was amazed how in sync the whole thing was despite all the layers. (It uses the same chain technique, but not "live".)

Not-live overdubbing with perfect sync has been going on since the dawn of multi-track recording, although the popularity of including video from each layer (and DIY without a tracking engineer running the session) surged in popularity during the pandemic. With modern editing in a DAW, quantizing every phrase, word, or even syllable to the grid (or other layers) isn't difficult at all, just a bit tedious.

Someone else in this thread linked to software like I described: https://github.com/gwillen/solstice-audio-test

I will try to search around and get you some more examples. I can't remember off the top of my head what else worked that way.

For which kind of music does this work in practice, though? The first musician in the chain would have a very lonely experience ;-)

Another technique is to mix all musicians on a server and send the mix back to all of them. Everyone hears the exact same signal, so in theory people could play perfectly in sync, but in practice hearing yourself delayed is very awkward and needs lots of training. We tried it but gave up quickly.

The first musician could be the conductor and they already are accustomed to conduct a bit ahead of the sound. Or they could put the instrument with most notes.

Musicians want/need to hear each other. This is obvious for improvised music, but even when everything is written out, players have/want to listen to each other.

While this approach certainly works from a technical perspective, but I don't see many musical styles where this would yield a satisfying musical result. However, it might work for pieces which are specifically written for this constellation.