Melancholy is a feeling, a strange feeling. It cames when you don't expect it. Usually cames because of a song, a memory in your heart or a picture.
The first one is a bit sad because of the melody, but it has a beautiful meaning.
This one is a bit melancholic for me, it's very beautiful and the melody is happy but the letter is kind of sad.
In general feelings appear to mark our heart our life.
: )