Tune: primarily audiovisual artist's medium (7)
I believe the answer is:
tempera
'artist's medium' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for tempera that I've seen before include "Paint made using egg-yolk" , "decorative style" , "vehicle" , "Painting method using emulsion" , "Egg-yolk and water painting medium" .)