private com.google.protobuf.SingleFieldBuilderV3<
              com.google.protobuf.Duration,
              com.google.protobuf.Duration.Builder,
              com.google.protobuf.DurationOrBuilder>
          getGopDurationFieldBuilder() {
        if (gopDurationBuilder_ == null) {
          if (!(gopModeCase_ == 9)) {
            gopMode_ = com.google.protobuf.Duration.getDefaultInstance();
          }
          gopDurationBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.protobuf.Duration,
                  com.google.protobuf.Duration.Builder,
                  com.google.protobuf.DurationOrBuilder>(
                  (com.google.protobuf.Duration) gopMode_, getParentForChildren(), isClean());
          gopMode_ = null;
        }
        gopModeCase_ = 9;
        onChanged();
        return gopDurationBuilder_;
      }
<pre>
Select the GOP size based on the specified duration. The default is
`3s`. Note that `gopDuration` must be less than or equal to
[`segmentDuration`](#SegmentSettings), and
[`segmentDuration`](#SegmentSettings) must be divisible by
`gopDuration`.
</pre>

<code>.google.protobuf.Duration gop_duration = 9;</code>
java-video-transcoder/proto-google-cloud-video-transcoder-v1/src/main/java/com/google/cloud/video/transcoder/v1/VideoStream.java