windows RT / Universal app, Text to speech "Save as Mp3"

I'm trying to make a speech to text universal app but got stuck on one thing. I looked all over the internet and could not find a proper solution which works.. So I came here.. Basically I want the app to save what ever is in the text box as mp3. Here is my code so far:

 private void Speak_Click(object sender, RoutedEventArgs e)
    {
        SpeakText(Text.Text);
    }
    public async void SpeakText(string TTS)
            {
                SpeechSynthesizer ttssynthesizer = new SpeechSynthesizer();

                //Set the Voice/Speaker
                using (var Speaker = new SpeechSynthesizer())
                {
                    Speaker.Voice = (SpeechSynthesizer.AllVoices.First(x => x.Gender == VoiceGender.Female));

                    ttssynthesizer.Voice = Speaker.Voice;
                }

                SpeechSynthesisStream ttsStream = await ttssynthesizer.SynthesizeTextToStreamAsync(TTS);

                //play the speech
                MediaElement media = new MediaElement();
                media.SetSource(ttsStream, " ");
            }