There is a trigger "OnTransitionIn" which can be used for reacting on an input if it is transitioning to the Output. Unfortunately, this doesn't help if some actions already have to change the input if it is sent to the Preview. A typical example is the activation of certain layers or the dynamic re-configuration of layers, where the result really have to be checked in the Preview phase before going live with it. Hence, I suggest that there are also triggers "OnPreviewIn" (and perhaps even "OnPreviewOut") or something, so one can perform enter (and leave) actions also for the important preview phase.

I've a complex greenscreen based setup with multiple cameras where the Virtual PTZ functionality cannot be used (because it acts only on the main layer and not the layers 1-10, but for greenscreen based cameras one needs always two layers: the chroma-key'ed camera in front of a rendered canvas) and instead I've to emulate the Virtual PTZ through a Position (PanX/PanY/Zoom).

When I now want to place a person in such a source virtual PTZ input over their slides in a PiP fashion I need another Position. As vMix does not flatten/pre-render layers except for Mix inputs, I have to use an intermediate Mix input between the source virtual PTZ input and the target scene input. As there are only a maximum of 3 Mix inputs and a lot more Virtual PTZ inputs, whenever I want to place the source Virtual PTZ input into the target scene, I've instead have to place the reusable Mix input into the target scene and use a trigger to let the Mix input show the intended source virtual PTZ input.

This works just fine for the Output with the "OnTransitionIn" triggers, but this way the operator gets rather confused when bringing the target scene into Preview, because at this time the embedded intermediate Mix input will usually still show the wrong source virtual PTZ input. As all scene changes are going over the Preview in our workflow, I really would like to make those adjustments to the Mix input when an input is brought into Preview. This way, in the Preview the operator can verify that it is really the correct scene which should be cut into Output afterwards. Without this, one has to believe that the scene will show the correct person once in Output. This is too nasty IMHO.

Shortcuts for all source virtual PTZ inputs to be placed into the Mix would be another option, but as the Mix input is just an intermediate one, the operation would have to remember that the target scene is based on an embedded virtual PTZ. In our productions the operation just steps through all the target scenes and everything is attached to those scenes. So I would like to also attach this Mix re-configuration to the target scene instead of having to setup dozens of extra Companion keys for the operator...