Campaigns with slides, .json

Both African Kingdoms and Rise of the Rajas use .json files for showing slides before their scenarios. Do any of you know how to do it for a custom made campaign?
I tried following the examples of the json of those campaigns, but it seems I’m stuck. Could anyone point me in the right direction?

Note: I’ve already know how to add scenario icons, modify their coordinates and icons and change banners and backgrounds with .json files. I’ve already posted this in aok.heavengames and reddit