Export slices, how to scale with Matte fill

[CM0]

I have hundreds of artboards I want to export and change the aspect ratio without distorting the image. So I want a Matte to fill the area that I expand the image width.

Is there no way to do this? Seems all scaling options stretch the image?

[v_kyr]

It's probably easier to do that after exporting sliced images from the artboards then, so to fill areas on a bulk of images. - One free tool predestinated for such tasks is ImageMagick, which nearly offers everything one can imagine in this regard.

With just using Affinity tools here instead things will get difficult and laborious. As first ADe doesn't offer any automation, or bulk processings except the Export Persona, and using the ADe files in APh then for applying some matte macros and bulk exporting can be adventurous.

There were some older threads where people needed some custom image size specific padding solution via APh, which might give you an overall idea here for using the Affinity apps or some third-party script solutions ...

 

... but all that can be done more easily via a tool like ImageMagick then.