My first pass would be to do it based on screentime.
My second pass would be to give the screentime ratios to the user, allowing them to tweak the ratios themselves.
Absolutely. Look at what Humble Bundle does, where you can tweak the proportion of your payment that goes to various things. That's still quite novel.
My first pass would be to do it based on screentime.
My second pass would be to give the screentime ratios to the user, allowing them to tweak the ratios themselves.