public Builder setMultiSpeakerMarkup(
        com.google.cloud.texttospeech.v1.MultiSpeakerMarkup value) {
      if (multiSpeakerMarkupBuilder_ == null) {
        if (value == null) {
          throw new NullPointerException();
        }
        inputSource_ = value;
        onChanged();
      } else {
        multiSpeakerMarkupBuilder_.setMessage(value);
      }
      inputSourceCase_ = 4;
      return this;
    }
<pre>
The multi-speaker input to be synthesized. Only applicable for
multi-speaker synthesis.
</pre>

<code>.google.cloud.texttospeech.v1.MultiSpeakerMarkup multi_speaker_markup = 4;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1/src/main/java/com/google/cloud/texttospeech/v1/SynthesisInput.java