public Builder mergeInput(com.google.cloud.texttospeech.v1beta1.SynthesisInput value) {
      if (inputBuilder_ == null) {
        if (((bitField0_ & 0x00000002) != 0)
            && input_ != null
            && input_
                != com.google.cloud.texttospeech.v1beta1.SynthesisInput.getDefaultInstance()) {
          getInputBuilder().mergeFrom(value);
        } else {
          input_ = value;
        }
      } else {
        inputBuilder_.mergeFrom(value);
      }
      if (input_ != null) {
        bitField0_ |= 0x00000002;
        onChanged();
      }
      return this;
    }
<pre>
Required. The Synthesizer requires either plain text or SSML as input.
</pre>

<code>
.google.cloud.texttospeech.v1beta1.SynthesisInput input = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/SynthesizeLongAudioRequest.java