In order to fastest drastically the render time of an animation, I would like to reduce render zone striclty to the animated one and complete the render with the static part of the image as a background. I though I could easily achieve this in the compositor but I failed (I’ve just started to tame this amazing application. I’m not an experimented user at all). My intuition was to simply compose the image using an " alpha over " node and an eventually “scale” one to forced sized. And then restrict the rendered zone on the camera. Though in the viewer node the result match the goal, the final render only produced an image corresponding to the restrict rendered zone, the rest of the image remaining transparent.
I can hardly imagine this goal couldn’t be achieved. It’s look like a nominal use case to me. Can anyone give the trick ?