Moved to InDesign EPUB forum.
Do you also have a solution Bob?
Not off the top of my head.
You have to preview somewhere else: iBooks app in OSX or Readium plug-in of Chrome browser.
Did you do the preview somewhere else?
Don't rely too heavily on the EPUB Preview Panel; it's not meant to be 100% accurate, and it has some limitations. Honestly, that's okay--you wouldn't want Adobe bloating InDesign by putting a fully functional EPUB reader inside it anyway.
You can also try a few other methods for media inclusion and hiding I cover in my new video courses on building reflowable and fixed-layout ebooks in InDesign. InDesign CC EPUB Building on the Fundamentals in particular spends a lot of time focusing on working with audio and video in EPUBs.
Also thanx for this answer Pariah, I can't wait to look at your videos,