I've a setup of four physical cams (BirdDog P400) and a tally light system (FlexTally). The setup is used for both greenscreen-based and regular productions. For the regular productions the cam inputs are directly used as layers in scene inputs. For the greenscreen-based productions I've to apply a chroma-key. In order to now having to re-configure (enable/disable the chroma-key filter) on the cam inputs, I use four corresponding "Virtual Inputs" of the four cam inputs and permanently apply the chroma-key filter there (other types of inputs cannot be used because the chroma-key filter is applied to the Main layer only). For the greenscreen-based productions the scene inputs just have to use the chroma-key'ed virtual inputs on their layers. This works just fine.

Unfortunately, for greenscreen-based productions the tally lights are dead. Because FlexTally requires that vMix tells it whenever the four physical cams are in Preview or Output. But the intermediate "Virtual Inputs" seem to break the transitive sequence of Tally information. When I telnet(1) to the vMix API and do a "SUBSCRIBE TALLY" I see that the target scenes are flagged and also the "Virtual Inputs", but the physical cam inputs are never flagged.

So, it seems like vMix accidentally or intentionally breaks/stops the transitive Tally information sequence on "Virtual Inputs". Unfortunately, this is the only way to apply a chroma-key without changing the original physical cam inputs all the time. At least as for as I know. As "Virtual Inputs" really show on ther main layer the content of the source input, I see no reason why the Tally information should not be passed through to the source inputs.

SITUATION CLARIFIED -- There is no need to take care of this request in forthcoming vMix versions.