getLiveEdge_() {
    goog.asserts.assert(this.presentationStartTime_ != null,
        'Cannot compute timeline live edge without start time');
    // Date.now() is in milliseconds, from which we compute "now" in seconds.
    const now = (Date.now() + this.clockOffset_) / 1000.0;
    return Math.max(
        0, now - this.maxSegmentDuration_ - this.presentationStartTime_);
  }
@return {number} The current presentation time in seconds.
@private