this piece of music has been used in various movies and tv shows over the years. i first heard it in the 1970 movie A LITTLE ROMANCE starring Laurence Olivier and a very young Diane Lane.
Another answer: I believe it's Lute Concerto in D major, RV 93, Largo. Google it and see whether that's what you're looking for.
Vivaldi's Concerto in D Major RV. 93, II-Largo
