保存文本到语音音频文件不起作用

Question

我根据此tutorial创建了一个Android TTS应用，并且我尝试将语音导出为.mp3或.wav或其他音频文件。我在Stackoverflow上尝试了many个答案，但没有人工作，因为我对它们并不了解。如果有人能帮我，我会非常感激。如果可以的话，请提供完整的代码！

import android.speech.tts.TextToSpeech;
import android.util.Log;

import android.view.Menu;
import android.view.MenuItem;
import android.view.View;

import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.util.List;
import java.util.Locale;

import android.hardware.Sensor;
import android.hardware.SensorManager;
import android.widget.Toast;

public class MainActivity extends Activity {
   TextToSpeech t1;
   EditText ed1;
   Button b1;

   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      ed1=(EditText)findViewById(R.id.editText);
      b1=(Button)findViewById(R.id.button);

      t1=new TextToSpeech(getApplicationContext(), new TextToSpeech.OnInitListener() {
         @Override
         public void onInit(int status) {
            if(status != TextToSpeech.ERROR) {
               t1.setLanguage(Locale.UK);
            }
         }
      });

      b1.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View v) {
            String toSpeak = ed1.getText().toString();
            Toast.makeText(getApplicationContext(), toSpeak,Toast.LENGTH_SHORT).show();
            t1.speak(toSpeak, TextToSpeech.QUEUE_FLUSH, null);
         }
      });
   }

   public void onPause(){
      if(t1 !=null){
         t1.stop();
         t1.shutdown();
      }
      super.onPause();
   }

   @Override
   public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.menu_main, menu);
      return true;
   }

   @Override
   public boolean onOptionsItemSelected(MenuItem item) {
      // Handle action bar item clicks here. The action bar will
      // automatically handle clicks on the Home/Up button, so long
      // as you specify a parent activity in AndroidManifest.xml.

      int id = item.getItemId();

      //noinspection SimplifiableIfStatement
      if (id == R.id.action_settings) {
         return true;
      }
      return super.onOptionsItemSelected(item);
   }
}