@java.lang.Override
  public com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkupOrBuilder
      getMultiSpeakerMarkupOrBuilder() {
    if (inputSourceCase_ == 4) {
      return (com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup) inputSource_;
    }
    return com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup.getDefaultInstance();
  }
<pre>
The multi-speaker input to be synthesized. Only applicable for
multi-speaker synthesis.
</pre>

<code>.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup multi_speaker_markup = 4;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/SynthesisInput.java