public Builder mergeMultiSpeakerMarkup(
        com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup value) {
      if (multiSpeakerMarkupBuilder_ == null) {
        if (inputSourceCase_ == 4
            && inputSource_
                != com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup.getDefaultInstance()) {
          inputSource_ =
              com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup.newBuilder(
                      (com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup) inputSource_)
                  .mergeFrom(value)
                  .buildPartial();
        } else {
          inputSource_ = value;
        }
        onChanged();
      } else {
        if (inputSourceCase_ == 4) {
          multiSpeakerMarkupBuilder_.mergeFrom(value);
        } 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.v1beta1.MultiSpeakerMarkup multi_speaker_markup = 4;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/SynthesisInput.java