Blunder in film describing special record (7)
I believe the answer is:
misstep
'blunder' is the definition.
(misstep is a kind of blunder)
'film describing special record' is the wordplay.
'film' becomes 'mist' (I've seen this before).
'describing' is an insertion indicator (describe can mean to form the outline of).
'special' becomes 'S' (common abbreviation as in Special Air Service).
'record' becomes 'ep'.
'mist' placed around 's' is 'misst'.
'misst'+'ep'='MISSTEP'
'in' is the link.
(Other definitions for misstep that I've seen before include "Badly judged move" , "Badly judged footing" , "False move" , "bad move" , "Error" .)