createPlayheadObserversForSrcEquals_(startTime) {
    goog.asserts.assert(this.metadataRegionTimeline_,
        'Must have metadata region timeline');
    goog.asserts.assert(this.video_, 'Must have video element');

    const startsPastZero = startTime instanceof Date || startTime > 0;

    /**
     * @type {!shaka.media.RegionObserver<
     *         shaka.extern.MetadataTimelineRegionInfo>}
     */
    const metadataRegionObserver = new shaka.media.RegionObserver(
        this.metadataRegionTimeline_, startsPastZero);

    metadataRegionObserver.addEventListener('enter', (event) => {
      /** @type {shaka.extern.MetadataTimelineRegionInfo} */
      const region = event['region'];
      this.dispatchMetadataEvent_(region,
          shaka.util.FakeEvent.EventName.Metadata);
    });

    // Now that we have all our observers, create a manager for them.
    const manager = new shaka.media.PlayheadObserverManager(this.video_);
    manager.manage(metadataRegionObserver);
    return manager;
  }
Create the observers for src equals playback. These observers are
responsible for notifying the app and player of specific events during src
equals playback.

@param {number|!Date} startTime
@return {!shaka.media.PlayheadObserverManager}
@private