Remember that text in an html document is about 2KB in size for contents of an average page in a book, or 200KB for 100 pages. The png image below is a little more than 400KB in size - about the same as this collection of short stories by James Joyce.
Victoria Harbor, Hong Kong, 2012
So when you consider putting something other than text in html up on a web site – pdfs, videos, audio files, animations, photographs, graphics – make sure:
It adds something text can not, otherwise it is a waste of time and bandwidth.
That its content is accessible to those who can’t see or hear it and that it will work on different devices.
That you are willing to have your site available only to those with a broadband connection, especially if what you have added is a video. (Less than 12% of the world's population have broadband, as compared with about a ⅓ who have an internet connection.)
Some additional issues to look at when using videos or animations for teaching in place of text, with or without illustrations, are:
How much more time does it take to watch and hear the information in a video or animation than to read it?
How easy is it to go back and review the material presented?
How easy is it to search for a word, a sentence, a name, a chart or a diagram that was shown?
How difficult is it to edit, update or correct a video or an animation as compared to text document?
How many specialized skills do the different media require to produce and edit them? Are they available? How much will they add to the cost?
