Video's margins upset film franchise (4)
I believe the answer is:
vote
'franchise' is the definition.
(synonyms)
'video's margins upset film' is the wordplay.
'margins' says to hollow out the word (remove centre letters) (the letters on the margins are used).
'upset' says the letters should be written in reverse.
'film' becomes 'et'.
'video' with its middle taken out is 'vo'.
'et' reversed gives 'te'.
'vo'+'te'='VOTE'
(Other definitions for vote that I've seen before include "Plebiscite" , "Register one's choice" , "Indicate choice in an election" , "Take part in an election" , "Formal indication of opinion in an election" .)