Group of actors keeping ready ahead of electronic recording (8)
I believe the answer is:
cassette
'recording' is the definition.
(I've seen this before)
'group of actors keeping ready ahead of electronic' is the wordplay.
'group of actors' becomes 'cast' (group of actors in a production).
'keeping' means one lot of letters goes inside another (some letters kept inside).
'ready' becomes 'set' (set can mean ready or prepared).
'ahead of' means one lot of letters go next to another (some letters go in front of others).
'electronic' becomes 'e' (as in e-mail or e-books).
'cast' placed around 'set' is 'cassett'.
'cassett'+'e'='CASSETTE'
(Other definitions for cassette that I've seen before include "Test case about tape container" , "Box of recordings" , "It may contain film" , "Tape unit" , "Audio tape holder" .)