private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.speech.v2.VttOutputFileFormatConfig,
            com.google.cloud.speech.v2.VttOutputFileFormatConfig.Builder,
            com.google.cloud.speech.v2.VttOutputFileFormatConfigOrBuilder>
        getVttFieldBuilder() {
      if (vttBuilder_ == null) {
        vttBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.speech.v2.VttOutputFileFormatConfig,
                com.google.cloud.speech.v2.VttOutputFileFormatConfig.Builder,
                com.google.cloud.speech.v2.VttOutputFileFormatConfigOrBuilder>(
                getVtt(), getParentForChildren(), isClean());
        vtt_ = null;
      }
      return vttBuilder_;
    }
<pre>
Configuration for the VTT output format. If this field is set, then
transcripts will be written to the sink in the VTT format.
</pre>

<code>.google.cloud.speech.v2.VttOutputFileFormatConfig vtt = 2;</code>
java-speech/proto-google-cloud-speech-v2/src/main/java/com/google/cloud/speech/v2/OutputFormatConfig.java