How to save SpeechSynthesisStream as audio in local storage of Windows Phone 8.1

I am using a SpeechSynthesizer class in my Windows Phone 8.1 Store app (XAML app/ windows runtime app/ universal app). It outputs a SpeechSynthesisStream which i need to save as a mp3/audio file in phone's local storage. Here's the code that i am using to generate the stream. How to save it as an audio file?

using (var speech = new SpeechSynthesizer())
{
      var voiceStream = await speech.SynthesizeTextToStreamAsync(text);
}