If you use Audible books, you can include them as well. I tend not to pay close enough attention when I am listening to a book for it to be the same thing. Years ago, when my wife and I published a monthly statewide newspaper for a year, it was a free newspaper supported by ads, although not well enough for us to continue it. I would drive throughout the state, dropping bundles off, and I would use Audible a lot while doing that. If it didn't annoy my wife, I might play Audible books at night because I can process things reasonably well while asleep, but to play a book otherwise, I find that I lose large portions of it.