public function getFrameHeight()
    {
        if (null === $this->frameHeight) {
            $match = [];
            preg_match(self::$REGEX_FRAME_WH, $this->output, $match);
            if (array_key_exists(1, $match) && array_key_exists(2, $match)) {
                $this->frameWidth = (int)$match[1];
                $this->frameHeight = (int)$match[2];
            } else {
                $this->frameWidth = 0;
                $this->frameHeight = 0;
            }
        }

        return $this->frameHeight;
    }