MPEG-1 (.mpg) or [VideoCD-MPEG1-flavor (.dat but authored)] are ideal. No codec, universal playback and high (but only non-interlaced) quality potential at bitrates that can fit on CD and amply on DVD. They can stretch a website somewhat by often needing twice the bandwidth of their codec-required(or player upgrade) equivalents.

Even MPEG-1 can be a problem (black picture or lip-sync) if folk have loaded additional software to that which came with their PC, Mac etc. Same goes for the transport you choose and how it might be reachable through corporate security solutions.

Making more than one type of media can help you reach more people where storage isn't an issue but improving your consumption of bandwidth is an issue.