To the audience a line from the more popular song (5)
I believe the answer is:
aside
This clue is a double definition.
'to the audience a line' is the first definition.
(a line in a play spoken to the audience)
'the more popular song' is the second definition.
(the A-side rather than the B-side of a record)
'from' acts as a link.
(Other definitions for aside that I've seen before include "Words spoken apart in an undertone" , "Remark not for hearing" , "Apart; incidental remark" , "Remark by an actor, directly to audience say" , "Privately, apart" .)