Sorry, that's fixed now. I accidentally had it cutting off at midnight UTC. I just pushed expiration out by another day (and it's now judged by Pacific time, and the page says that explicitly for good measure).
ps: as usual, your video (compression) was a joy to watch, you should be a Khan Academy partner, or host a university or be a mars overlord. Something like that
I don't work with distributors at all because they tend to (a) want some level of control over content and/or the legal right to modify and reuse it, (b) offer unfavorable royalty rates, and (c) have mixed quality levels between the works they host. I like that DAS is a comparatively small body of work that people know by name and trust to be good.