A company sells audio books and provides its consumers with an app that interprets the speech in the audio books on the fly back into text to show on the screen

A company sells audio books and provides its consumers with an app that interprets the speech in the audio books on the fly back into text to show on the screen: publishers claim copyright infringement. A company sells an app that, given speech in any form by a user, including any audio book format, interprets the speech on the fly back into text to show on the screen: what's the difference? what do publishers claim in that case? Please, enlighten me.