Sorry for the title, I find it quite hard to describe what I want to do in a single sentence

We have a few TV here linked to our computer, which we use to display clips about what we do in our sport center, what you should do to stay in good form ect ... It's running non stop, actually though vlc + playlist. Those main clips are 1-2 hours long and we have about 20 of them looping randomly all day.

We would like to inject ads for some of our sponsiored products every now and then during the playlist, like say one ad every 15 minute.

Does any one know how we can do that, while keeping the main clip random order ?

I thought about encoding the whole thing as a single movie with ads inserted, but then it's not random. So we can put the ads in the playlist itself right ? Except clips are several hours long and we want that more often than that.

Cutting the main clips in several pieces seems to work but that kind of sucks as new clips are made every month.

If any one has an idea, thanks a lot