Amount or length of film (7)
I believe the answer is:
footage
I believe this is a double definition.
'amount' is the first definition.
(I have seen 'amount of film' mean 'footage' so perhaps 'amount' could also mean 'footage')
'length of film' is the second definition.
(I've seen this before)
(Other definitions for footage that I've seen before include "Part of film" , "Length of film" , "Film that has been shot" , "quantity shot" , "amount of film" .)