Film South American capital? Not half! (5)
I believe the answer is:
video
'film' is the definition.
(I've seen this before)
'south american capital? not half' is the wordplay.
'south american capital?' becomes 'montevideo' (I've seen this in another clue).
'not half' suggests halving the letters.
'montevideo' halved is 'VIDEO'.
(Other definitions for video that I've seen before include "(Tape for) recorder of film etc" , "Who killed the radio star? (5)" , "YouTube media" , "Capture on film" , "Film recording" .)