sync slideshow with screenshot filter ? (or how to use different files with the same image mask)

[novelscale]

Hello, is there a way to grab a screenshot everytime the slideshow change the image - and so on ?
The small lag created if I do this manually increases during the hour and they get unliked.

The reason I came to this was looking for a way to use different image files as "image mask" file, so I start the slideshow and output the screenshot to the same file. Then I use the name of this file as image mask source and the image mask changes automatically.

I'm not sure if there's a better way to do this, is there ?

thanks