I'm pretty sure this isn't semantic. I expected that the footnotes would be in the source when I went to view it and they're not. It's a fun video metadata demo, but it's not semantic HTML.

The demo is "semantic video", not "semantic HTML".

The video tag references a "data-timeline-sources" document at http://www.rebelliouspixels.com/semanticremix/data.xml with all the footnotes.