If you have a Video on Youtube, Vimeo, etc. you'd like to reference, the youtube-dl or you-get utility can be used to make a offline copy.
wget \ --no-clobber --page-requisites --html-extension \ --span-hosts --convert-links --restrict-file-names=windows \ --domains gtalug.org --no-parent https://wiki.gtalug.org/guide_to_presenting
You can added the
--recursive
argument to download the entire web site.