Our videos are hosted by Vimeo. Over the last several years they have never failed us!  However, of course it is possible that an issue arises. The Internet is full of surprises! If videos are not streaming, rest assured we will do everything we can to get things back up and running as quickly as possible. We cannot guarantee that our videos will always work and that there will never be any unexpected downtime, however so far we haven't had any issues.
One exception we know of is CHINA.  Due to the Chinese government's internet censorship policy, our video books cannot be streamed in China! This is very disappointing for Chinese customers who contact us wishing to use our resources to learn French :(