Weakness accepting nothing finished in narration (5-4)
I believe the answer is:
voice-over
'narration' is the definition.
(I've seen this in another clue)
'weakness accepting nothing finished' is the wordplay.
'weakness' becomes 'vice' (a moral weakness).
'accepting' means one lot of letters goes inside another (inserted letters are accepted).
'nothing' becomes 'O' (O resembles 0).
'finished' becomes 'over' (over can mean finished or ended).
'vice' going around 'o' is 'voice'.
'voice'+'over'='VOICE-OVER'
'in' is the link.
(Another definition for voice-over that I've seen is " Narration to a film".)