Amazon has enhanced their Texbook Creator app with the ability to embed audio and video. Publishers will be able to include image pop-ups and have their final product compatible with the Kindle Fire line of tablets and the Amazon app for Android and iOS.
The Textbook Creator is fairly bare-bones right now, it only accepts PDF source files. Amazon is testing functionality for Microsoft Word documents, EPUB, and HTML, but there is no word on when the PC or MAC app will be updated again.
I think what Amazon is trying to do is eventually have a robust solution like Apple has for their iBooks Author program. Many of the top publishers use the Apple solution because its easier to sell content on the App Store or via iBooks.