@java.lang.Override
    public boolean hasMultiSpeakerMarkup() {
      return inputSourceCase_ == 4;
    }
<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>

@return Whether the multiSpeakerMarkup field is set.
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/SynthesisInput.java