How to mark transparent to be black background?

[H5T7P4]

Hello,

is it possible to mark transparent background as black in XnConvert.

In GIMP you can mark a background color and then export the image
as you can see here:

https://youtu.be/2PPwLad8whg?t=250

The background is still transparent in the image but there seems then to be a marker
that the background should be black.

I installed the BIMP plugin for GIMP to do this in a batch. But I didn't find a way to do it.

So can XnConvert manipulate a image in this way (only set a marker for the background color in the image
but let background transparent)?

If yes: How can it be done?

[xnview]

sorry but not posible

[H5T7P4]

sorry but not posible

Ok, thank you.