text to speech offline

There has been a built-in text to speech API in iOS since version 7. It does not require a web or Internet connection to use in an iOS app.

This is a link on how to use the built-in iOS text to speech API with Objective-C in Xcode. http://useyourloaf.com/blog/2014/01/08/synthesized-speech-from-text.html

This is a link on how to use the built-in iOS text to speech API with Swift in Xcode. http://www.appcoda.com/text-to-speech-ios-tutorial/

One of the current drawbacks of using the built-in iOS text to speech API is that you do not have the ability to choose the gender of the text to speech voice. You are stuck with the default gender of the language country. For example, you currently cannot change a US English voice from female to male or change a UK English voice from male to female. The voices currently being used for the built-in iOS text to speech API are VoiceOver voices and not Siri voices.

If you want to try a third-party solution for a text to speech API for your iOS app, you may want to look at Acapela TTS for iOS. Their website address is http://www.acapela-group.com/acapela-for-ios/.