public function getPixelAspectRatio()
    {
        if ($this->pixelAspectRatio === null) {
            $match = [];
            preg_match(self::$REGEX_PIXEL_ASPECT_RATIO, $this->output, $match);
            $this->pixelAspectRatio = (array_key_exists(1, $match) && array_key_exists(
                    2,
                    $match
                )) ? ($match[1] / $match[2]) : 0;
        }

        return $this->pixelAspectRatio;
    }