You can do it, you just can't expect ePUB readers to support it, because the ePUB spec does not require them to do it (as if requiring was a guaranty for anything
). What I'd do, if I had to include some audio/video content, is provide, as a fallback, a page saying "The reading software does not support playing audio/video files, But you can watch/listen to this content in http://whatever" (that is, if nothing better is possible). That way, in the event some reader supports this, it will be played, but other readers will always have somethin useful instead.