Here’s a list of EPUB3 features supported in the initial Beta release. As we add features we’ll update this list as well as mention it in the Forums and Announcements area.
Reflowable and Fixed Reading Layouts
Images: JPG, PNG, GIF
Audio: MP3, M4A
Video: MP4 with H.264 Codec
Text Types: EPUB style sheets as CSS
Spine Level Content
These features will be supported in the near future: