code: public void start() {
      try {
        if (null == recorder) {
          recorder = new MediaRecorder();
          recorder.setAudioSource(MediaRecorder.AudioSource.DEFAULT);
          recorder.setOutputFormat(MediaRecorder.OutputFormat.DEFAULT);
          recorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
          recorder.setOutputFile(this.localPath);
          recorder.prepare();
        } else {
          recorder.reset();
          recorder.setOutputFile(this.localPath);
        }
        recorder.start();
        startRecordTime = System.currentTimeMillis();
        if (null != this.listener) {
          this.listener.onStartRecord();
        }
      } catch (IOException ex) {
        LOGGER.e("failed to start MediaRecorder. cause: ", ex);
      }
    }
docs: Begins capturing and encoding data to the file specified.