Legacy media at the start is not in retreat (8)
I believe the answer is:
heritage
'legacy' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for heritage that I've seen before include "Birth-related condition" , "historical collection?" , "Valued survivals from the past" , "Ancestry" , "Received culture and background" .)