protected onUpdateMetadata(event): void {
    if (!this.mediaElement) {
      Log.warn("MediaElement is null, ignore event (" + event.type + ")");
      return;
    }
    if (!this.metadata) {
      Log.warn("Metadata is null !!! ( implementation error )");
      return;
    }

    if (
      !(
        this.mediaElement.audioTracks &&
        this.mediaElement.videoTracks &&
        this.mediaElement.textTracks
      )
    ) {
      Log.warn("Tracks not implemented !!! ( implementation error )");
      return;
    }
    let signature: string = JSON.stringify(this.metadata);
    this.updateTracks();
    if (JSON.stringify(this.metadata) !== signature) {
      this.mediaChannel.onUpdateMetadata(this.getMedatadata());
    }
  }