A hundred in total seeing film (4)
I believe the answer is:
scum
'film' is the definition.
(I know that scum is a type of film)
'a hundred in total' is the wordplay.
'a hundred' becomes 'C' (Roman numeral).
'in' is an insertion indicator.
'total' becomes 'sum' (synonyms).
'c' placed into 'sum' is 'SCUM'.
'seeing' is the link.
(Other definitions for scum that I've seen before include "Floating film of filth" , "Floating muck" , "Worthless group of people" , "Impurities on surface of liquid, or rotten people" , "Impurities on liquid's surface" .)