Inception filming location? (5)

I believe the answer is:

onset

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'inception' is the definition.
(I've seen this before)

'filming location?' is the wordplay.
'filming' becomes 'on' (I can't justify this - if you can you should believe this answer much more).
'location?' becomes 'set' (set is a kind of location).
'on'+'set'='ONSET'

Can you help me to learn more?

(Other definitions for onset that I've seen before include "Cast stone in attack" , "Beginning; violent attack" , "17 down [ASSAULT]" , "Stone (anag)" , "Appearance of" .)

I've seen this clue in The Telegraph.

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