What does it means to write a book (i.e., a bookc), given that you can't assume it will be packaged as a bookp? The question is important, because I can't very well author a book if I don't know which content forms I'm permitted to include and which I'm not.
My answer to this question, perhaps counterintuitively, is based on a bookp. Whatever it means to write a "book," the result should be recognizable as what we currently understand a book to be. We could call TV "radio with pictures," but we don't, and we could call theatrical plays "live TV," but we don't do that, either. I don't see any sense in defining "book" such that somebody familiar with a bookp wouldn't be able to see the connection between what they know and what I've defined.
So here's my initial working definition of a book (i.e., a bookc): it can be reasonably represented as a bookp. That is, if I say "I'm writing a book," you can assume that whatever I produce can be reasonably represented in ink-on-paper form. So we're talking static content. All the usual book stuff is included, i.e., text, diagrams, tables, pictures, etc. Dynamically generated content is out. So are interactive elements. But audio, video, and animations may make the cut, depending on the form they take.
A video of a talking head, for example, can be represented in a bookp as a frame from the video (i.e., a photo of the speaker) accompanied by a transcript of what the speaker says. Readers lose the sound and cadence, etc., of the speaker's voice, and they're deprived of seeing how the speaker's face moves as he or she talks, but -- assuming such information was never the point of the video -- the essential content has been preserved in ink-on-paper form. Talking head videos are thus permissible in a bookc (and would be delivered as such on output devices where that's possible).
Similarly, transcripts of the audio-only equivalent of talking heads ("speaking voices?") make such audio permissible in a bookc. Many podcasts could thus be considered bookc manifestations. (If books in recorded form (i.e., audiobooks) are still books, then textual representations of speech are still speech ("textaudio"?), and since textual representations of speech can be published as recognizable bookps, recorded speech is legit in a bookc.) The way people express things in spoken versus written form typically differs qualitatively, so transcribing spoken audio and publishing it in book form is likely to yield a lousy book, but my goal here is to figure out what's in my author's toolbox and what's not. If something's in, part of my job as an author is to make sure I don't just use it willy-nilly; I'm responsible for using it well.
I find animations to be a particularly interesting case. As a book author, may I include animations? Consider, for example, David Howard's animation of the behavior of a red-black tree. Can such an animation be part of a bookc?
I'm inclined to think that it can. Books have long contained "before" and "after" diagrams to help explain how a transformation between two states occurs. You'll find several in the Wikipedia entry for red-black trees. (Well, you will if you look right now. What the page will look like if much time has elapsed between when I write this and you read it is anybody's guess.) It's easy to imagine such diagrams being frames extracted from an animation. If, as an author, I have enough conditional content control to be able to say
if (rendering for a device that can show animation)then at least some animations are within the purview of a bookc.
show this animation along with this explanatory text
show these animation frames along with this other explanatory text
The set of acceptable entities in a bookc is thus a superset of those that are directly expressible in a bookp. The information content of everything in a bookc must be representable in a bookp, but if a trivial tranformation needs to be applied (e.g., video is replaced by a selected frame, audio of speech is replaced by a transcript) or even if a nontrivial-but-straightforward transformation needs to be applied (e.g., animation + description replaced by animation frames + alternate description), such content is still valid, hence part of my toolkit as a book author. Writing a multiple-platform bookc thus gives me more choices for expressing myself than I'd have if I restricted myself to bookp publication.