private com.google.protobuf.SingleFieldBuilderV3<
              com.google.protobuf.Duration,
              com.google.protobuf.Duration.Builder,
              com.google.protobuf.DurationOrBuilder>
          getGopDurationFieldBuilder() {
        if (gopDurationBuilder_ == null) {
          if (!(gopModeCase_ == 8)) {
            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_ = 8;
        onChanged();
        return gopDurationBuilder_;
      }
<pre>
Select the GOP size based on the specified duration. The default is
`2s`. Note that `gopDuration` must be less than or equal to
[segment_duration][google.cloud.video.livestream.v1.SegmentSettings.segment_duration],
and
[segment_duration][google.cloud.video.livestream.v1.SegmentSettings.segment_duration]
must be divisible by `gopDuration`. Valid range is [2s, 20s].

All video streams in the same channel must have the same GOP size.
</pre>

<code>.google.protobuf.Duration gop_duration = 8;</code>
java-video-live-stream/proto-google-cloud-live-stream-v1/src/main/java/com/google/cloud/video/livestream/v1/VideoStream.java