Start where filming takes place (5)
I believe the answer is:
onset
'start' is the definition.
(both can mean the beginning of something)
'filming takes place' is the wordplay.
'filming takes' becomes 'on' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'place' becomes 'set' (setting is a kind of placing).
'on'+'set'='ONSET'
'where' acts as a link.
Can you help me to learn more?
(Other definitions for onset that I've seen before include "Attack using stone" , "origin" , "First signs" , "Storming" , "Beginning (of something often unpleasant)" .)