Capture on cassette (4)
I believe the answer is:
tape
'capture on cassette' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tape that I've seen before include "The finish line" , "Strip of material (that might be red!)" , "Race finishing-line" , "Breast this first to win a race" , "Bind" .)