private com.google.protobuf.SingleFieldBuilderV3<
            com.google.protobuf.Duration,
            com.google.protobuf.Duration.Builder,
            com.google.protobuf.DurationOrBuilder>
        getTotalBilledDurationFieldBuilder() {
      if (totalBilledDurationBuilder_ == null) {
        totalBilledDurationBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.protobuf.Duration,
                com.google.protobuf.Duration.Builder,
                com.google.protobuf.DurationOrBuilder>(
                getTotalBilledDuration(), getParentForChildren(), isClean());
        totalBilledDuration_ = null;
      }
      return totalBilledDurationBuilder_;
    }
<pre>
When available, billed audio seconds for the corresponding request.
</pre>

<code>.google.protobuf.Duration total_billed_duration = 6;</code>
java-speech/proto-google-cloud-speech-v2/src/main/java/com/google/cloud/speech/v2/RecognitionResponseMetadata.java