Well OCRing books (for book search) was found to be fair use because “book search” and “books” are in different markets. So to the extent it is like book search that could be in its favor.
Your other example (text to speech and audio books) is significantly less transformative as audio books and books are basically the same or very related markets. (For example they are both sold in the same specialty stores)
Is that legally any different from OCRing a copyrighted book? Or maybe running an audiobook through speech-to-text..