private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup,
            com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup.Builder,
            com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkupOrBuilder>
        getMultiSpeakerMarkupFieldBuilder() {
      if (multiSpeakerMarkupBuilder_ == null) {
        if (!(inputSourceCase_ == 4)) {
          inputSource_ =
              com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup.getDefaultInstance();
        }
        multiSpeakerMarkupBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup,
                com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup.Builder,
                com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkupOrBuilder>(
                (com.google.cloud.texttospeech.v1beta1.MultiSpeakerMarkup) inputSource_,
                getParentForChildren(),
                isClean());
        inputSource_ = null;
      }
      inputSourceCase_ = 4;
      onChanged();
      return multiSpeakerMarkupBuilder_;
    }
<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