Apple Pages doesn’t (yet) support HTML in any form, but iBooks Author does support creating the Epub / Fixed layout format. You’ll start by exporting as a Dashboard / iBooks Author Widget…
Choose a templated in iBooks Author:
Then drag your .wdgt file generated in the first step onto your book:
You’ll notice that you won’t have any option but to have your HTML widget centered on the page, but you do have the option of playing it when visible, as opposed to having the main timeline of scene 1 playing when clicked.
This page (for Pages / Epub export) does not mention HTML anywhere: https://support.apple.com/en-us/HT202066, but it is possible this feature is coming to Pages if Apple continues to take digital book creation seriously.