The background will be on the background layer of the ME bank. Doing it in a DSK would just be bizarre. If you wanted different backgrounds on the same output, you'd probably go down the split ME route, where you tie up two MEs doing the same thing, just with different backgrounds and feed those MEs out as the programme feed for each outlet.
So a Viz engine would be feeding the gallery a background rather than downstream.
The whole way the graphics engines are setup here are confusing and that’s why I was wondering if it was downstream. And could Mosart and BNCS handle that?
Yes - the galleries have dedicated Viz engines for DVE box backgrounds, full-screen still images etc. Those are cut/routed by the gallery vision mixer and are present on all outputs. For DVE boxes the Viz generating the box background is likely to be upstream keyed within an ME bank, possibly using resizers rather than a DVE, (or it could be fed into a DVE background channel if the DVE can be used independently of an ME bank, and is itself a source). There are many ways of skinning that cat on a modern mixer - and your options vary depending whether you are Sony, GVG original, GVG Kahuna etc.
Because you may need to feed things to in-vision screens as well as cutting them to air - doing all of that downstream wouldn't make sense.
Additionally there are additional overlaid Viz engines downstream of the gallery vision mixer that key on different on-screen furniture (lower thirds, flipper, clock, channel logo etc.)
Okay that answers another thing so full screen graphics are the same if they’re going out on two different styles?
Also I seem to remember (or dreamed) a post where Victoria Derbyshire Show went out as a simulcast but due to breaking news BBC Two remained with her custom package while News went with their style.
Don’t let anyone treat you like you’re a VO/SOT when you’re a PKG.