Display filtered list of items on item view

One more question :
For one of my auto-relation field i point to a category call "medias" with 2 sub cats called "photos" and "videos".
Is there a way to display articles from photos and videos when medias is choosed in item form (as caterogy for filtering auto relation).
I don't see any option for that ...
I also tried to enable multi in category selector (to choose photos and videos) but when i save item this field remain blank ...