This library use the Google Voice API and the Speex audio codec for speech-to-text on iOS
Google speech to text api v1 has been deprecated and google has release v2 which requires api key.For details see this github repository
You can get the api key by following the steps defined here
All you need to do is to open "SpeechToTextDemo-Prefix.pch" from sample project and set your api key.
For details see this blog post http://ideamakerz.com/mzeeshanid/ios-speech-to-text/