This is a question I debated with a writing buddy. I maintained they were not; the other party took a contrary position.
UNESCO defines a book as a non-periodical printed publication of at least 49 pages excluding covers.
Oxford English dictionary, as a written work published in printed or electronic form.
Merriam-Webster, as, a set of written sheets of skin or paper or tablets of wood or ivory: a set of written, printed or blank sheets bound between a front and back cover.
I conceded that maybe the current definitions of a book are out of date. Maybe, to meet modern usage, we may have to split the traditional definition?
An audio recording qualifies as a book in one respect. It stores language. Books store language. That works for when you can generate hard copy. Streaming doesn't generate hard copy. I can't stick a streamed title on a physical shelf along with a paperback and DVD. So does non-physical transmission qualify as a book? Audio recordings store and facilitate the transmission of literature. So audio recordings may not meet the physical definition of a book, but they meet the purpose of a book.
However, if Putin pushes the button, causing an electromagnetic pulse to wipe out all computers, you can forget about audiobooks because they'd cease to exist. And if Xi Jinping invades Taiwan and disrupts global microprocessor distribution, then in very short order you'll have nothing on which to play your DVDs.
But unless an asteroid collides with earth, traditional books will survive to preserve the wonders of our culture. And if the asteroid does strike, then books will still survive carved on stone. An option not currently offered by Amazon.
I rest my case.