public function getAudioBitRate()
    {
        if ($this->audioBitRate === null) {
            $match = [];
            preg_match(self::$REGEX_AUDIO_BITRATE, $this->output, $match);
            $this->audioBitRate = (int)(array_key_exists(1, $match) ? ($match[1] * 1000) : 0);
        }

        return $this->audioBitRate;
    }