I'm a system integrator, an installer for video production systems. I cater mostly to town halls and cable access. During the "bat flu" most towns resorted to Zoom, Microsoft Teams or other virtual meeting software for their public town meetings. Once everyone returned to the office, it was back to the installed production systems—only now everyone wants to fold the virtual meeting (I'll call it VM) into the works.

This sort of "hybrid" meeting creates the same problems once encountered by radio broadcasters when taking a phone caller live on the air. The telephone is a full-duplex system, with two send/receive channels in use. Telephone users can interrupt each other. But broadcast radio is half-duplex (or less) with only one send/receive channel, and used only one-way. To bridge the two systems required a box known as a "hybrid."

In audio and video production, there is already a technique known as "mix-minus" that allows the withholding of selected audio to avoid feedback—namely, suppressing microphones from the return feed to the studio. But how do you "mix-minus" with video? If you send the same PGM video to the VM participants that goes to the cable TV audience, it will produce "video feedback"—a hall-of-mirrors effect like the Doctor Who titles, or one of Nam June Paik's creations.

(If you are using vMix's Zoom plugin, all of this is fixed already. But not everyone uses Zoom for an installer's convenience.)

There are numerous approaches to the problem. Some simply keep the two systems separate. VM participants appear on a big screen for the local audience. And cable TV audiences have to suffice with a camera pointed at the screen open-air. This is not an ideal arrangement, especially if a text document is being "screen shared" among the VM users. I once assembled a two-switcher system for one client. Although instead of switching two shows in parallel, I set up one switcher as the "primary," which cut between all the various sources, except the VM source. The primary PGM was fed to the VM participants. Another copy of the PGM fed a secondary switcher to the cable TV audience, only it was a simpler A/B switch, cutting between the primary and the VM source whenever the cable TV audience needed to see them.

I've also beat my head on the possibility of using macros and scripts, which a system like vMix can do. When suddenly a simpler approach occurred to me, an approach almost any video switcher can do. And I was too wrapped up in cool, high-tech solutions to realize it before now:

Use the VM source strictly as a full-screen overlay, like a title. Never cut to it or take the VM directly. If the return feed to the VM audience is a "clean feed," which most switchers can do, they get the bonus of a fully intercut show, but never video feedback.

Some users may have more exotic "two output" requirements. They'll most likely have to resort to the two switcher method (or use a multi-M/E switcher like Blackmagic's ATEM). But for all my usual clients, this overlay and clean feed technique is easier, simpler, and less confusing to use.