If you like music or pop songs, you should have heard of this music piece or similar melody in movies or songs composed by Bettles, 李健,樸樹...
It calls " Pachelbel's Canon" or " Canon in D".
Johann Pachelbel (1653-1706) was a German composer in Baroque era.
Like most of his works, this one remained unknown for centuries.
At 1968, it suddenly gained popularity.
Since then, the elements of the piece, especially it's chords progression were used in a variety of pop songs.
It is the most popular music in wedding.