Unfortunately this is a known issue in iOS11. We filed a bug when one of our users hit this issue in a beta version of iOS 11 but we have not received an update on that report. There's also a discussion on the Apple support site: https://discussions.apple.com/message/32262178#32262178
After some testing, here's what I recommend:
External Video, such as Vimeo and Youtube embeds:
- Click Insert rectangle in Hype, and paste the
<iframe> code within the Inner HTML of that rectangle (don't put this inside of an HTML widget, because this will result in a double iframe)
- When dropping the HTML widget into iBooks author, use these settings in the Widget > Interaction settings:
For the iframe page, I wasn't able to get this working at all unfortunately.
Here's a test document I used: https://cl.ly/3Q002g3l0Z2q