According to their Reddit, it's going to ggo offline in the next week or two.

https://www.reddit.com/r/infinitejukebox/comments/5wh9hn/met...

The visualization is known as a chord diagram[1][2], and these particular ones generated by Echo Nest show repetitions in the analyzed songs (e.g. chorus lines). A circle is a good starting visualization because there is a linear progression from beginning to end (single path) and the chord diagram lends itself well to the metrics Echo Nest is demonstrating.

[1] http://www.datavizcatalogue.com/methods/chord_diagram.html

[2] https://bl.ocks.org/mbostock/1046712

Their FAQ: http://labs.echonest.com/Uploader/faq.html

It basically keeps the song going by jumping around to different parts that match within the song. It can lead to interesting effects (different extended solos, jumping around between choruses). It keeps the song going forever.

To start click at the top of the circle after selecting a song.

You can upload a song, and it will jump through the song backwards and forwards such that the song will seamlessly continue forever.