There are more ways to do that. I think the simplest one is:
Action: Format Value
Field: YEAR
Formatstring: $left(%year%,4)
This gives you simply the leftmost 4 characters %year%.
When "1867[cd][mv] Wiener Philharmonic Orchestra - An Der Schönen Blauen Donau" is not the YEAR tag-field you have to replace %year% with the appropiate field name. When it is the filename use $left(%_filename%,4).