Film buff is at a broadcast (8)
I believe the answer is:
fantasia
'film' is the definition.
(I've seen this before)
'buff is at a broadcast' is the wordplay.
'buff' becomes 'fan' ('fan' can be a synonym of 'buff').
'broadcast' indicates an anagram.
'is'+'at'+'a'='isata'
'isata' with letters rearranged gives 'tasia'.
'fan'+'tasia'='FANTASIA'
(Other definitions for fantasia that I've seen before include "animated film" , "Musical composition of several familiar themes" , "D [Disney] made" , "Disney film (1940)" , "Free invention" .)