Ok, I figured out a workaround.
1. (Select Movie files) > Paste the expression into a temporary field that will hold the sorted Actors values. I used Comment, since it's empty for all of my movies. Verify that this worked.
2. (Select movie files) > Library Tools > Move/Copy fields . Tell it to copy from Comment to Actors. Press OK.
That should do it. Try it with a couple of movies first to verify that it works. Undo is your friend.
Brian.
I understand you! but I've found a simply system.
1) select many different videos with this actors field problem.
2) apply =listsort([Actors]) in the same ACTORS field and press intro.
3) UN-check ALL actors but NOT this item: =listsort([Actors]) and press intro.
4) now appear the list of actors sort ok! all ok for ALL VIDEOS!! no need one by one. sometimes I can see the field "=listsort([Actors])".
5) un-check "=listsort([Actors])". Now only actors name is there.
finish. Not need copy between 2 fields!