public Builder mergeTotalBilledDuration(com.google.protobuf.Duration value) {
      if (totalBilledDurationBuilder_ == null) {
        if (((bitField0_ & 0x00000002) != 0)
            && totalBilledDuration_ != null
            && totalBilledDuration_ != com.google.protobuf.Duration.getDefaultInstance()) {
          getTotalBilledDurationBuilder().mergeFrom(value);
        } else {
          totalBilledDuration_ = value;
        }
      } else {
        totalBilledDurationBuilder_.mergeFrom(value);
      }
      if (totalBilledDuration_ != null) {
        bitField0_ |= 0x00000002;
        onChanged();
      }
      return this;
    }
<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