getSegmentAvailabilityDuration() {
    if (!this.isLive()) {
      shaka.log.warning('getSegmentAvailabilityDuration is for live streams!');
      return null;
    }

    if (this.manifest_) {
      const timeline = this.manifest_.presentationTimeline;
      return timeline.getSegmentAvailabilityDuration();
    } else {
      shaka.log.warning('No way to get segment segment availability duration!');
      return null;
    }
  }
Get the presentation segment availability duration. This should only be
called when the player has loaded a live stream. If the player has not
loaded a live stream, this will return <code>null</code>.

@return {?number}
@export