The obvious route — putting the callers on a bus and sending that bus to Master with the M button — doesn't work for callers: vMix deliberately excludes any bus sent to Master from the callers' return feed (otherwise mix-minus would break), so the callers would stop hearing each other.

The more complex setups I've seen solve it externally — each call out on its own bus to a hardware desk/Dante, build the mix-minus there, feed program-minus back per caller. Works, but it eats buses fast (an out and a mix-minus bus per caller) and assumes you've got the desk.

For a pure in-the-box setup, the only clean idea I can come up with is to leave the callers on Master (so mix-minus stays intact) and drive their faders together via the API — one action firing SetVolume on each caller's GUID at once, or mapping a single controller fader to several caller inputs. In theory that's group control without touching the bus routing. I haven't confirmed whether one physical fader maps cleanly to multiple SetVolume targets at the same time — has anyone done that, and does it hold up live?

For context, here's the rest of the setup I worked through, in case it helps anyone untangle the logic:

You add the input via Add Input → Video Call, and for each caller you use "Host a Call" — you're the host, and each guest connects with the URL and password vMix generates. The nice part is the audio: vMix mixes it automatically so a caller's own voice isn't sent back to them, which is what would otherwise cause feedback. So there's no complicated routing to build — it more or less explains itself once you see it that way.

Next question I ran into: what happens to a caller's audio when they're not on screen? If you switch between different shots, the audio drops out with the picture. The fix: once the call is created, double-click the input, go to the General tab, and uncheck "Automatically mix audio". Now the audio stays on wherever you've enabled it, independent of the picture — and from there you can also send a caller to a separate bus for processing or an external feed, while still bringing their video in as an overlay.

On the display side, one limitation worth knowing: the Layer 1/2/etc. positions don't apply when you bring an input in as an overlay — the overlay uses the input's Main position. So I set the position on the Main of the call input, which means that guest can't also go full screen at the same time. Not a big deal for a commentator who's meant to stay small anyway. For richer layouts I add a background graphic as an input and use Layers to arrange the callers on top — pick a 2- or 4-box preset, drop the guests/host in, and build a few of those as separate scenes. Then you can switch between one guest, two guests, three guests, or cut a single guest in to comment over a video. Between that and the simple overlay you've got pretty much every situation covered.

One thing not to forget: if you send a guest to an additional separate bus for processing, don't route that bus back into Master — same mix-minus trap as above.

So the only open piece for me is the group-leveling question at the top — would love to hear how you handle it.