I really love this song, so I'd like to share with you people here. :)
It's a composition of Joe Hisaishi, the composer for Miyazaki's (宫崎骏) famous Japanese cartoons.
Here's the audio sample.
Do note that the video and the audio sample sounds a little different.
Usually when those artist perform live, they'll alter the song a little to give audience a little surprise. :)