public function getAudioSampleRate()
    {
        if ($this->audioSampleRate === null) {
            $match = [];
            preg_match(self::$REGEX_AUDIO_SAMPLE_RATE, $this->output, $match);
            $this->audioSampleRate = (int)(array_key_exists(1, $match) ? $match[1] : 0);
        }

        return $this->audioSampleRate;
    }