And as I mentioned in the overlays section, there are reading systems that already give word-level text-audio synchronization in synthetic speech playback mode, surpassing what most people would attempt with an overlay and human narration. As each word is fed for rendering it gets highlighted on the screen auto-magically; there’s nothing special you have to do.

The cost and effort to improve synthetic speech is also one that has the potential to decrease over time as you build re-usable lexicons and processes to enhance your books.

But enough selling of benefits. You undoubtedly want to know how EPUB 3 helps you, so let’s get on with the task.

The new specification adds three mechanisms specifically aimed at synthetic speech production: PLS lexicon files, SSML markup, and CSS3 Speech style sheets. We’ll go into each of these in turn and explore how you can now combine them to optimize the quality of your ebooks.