public function setBitrate($bitrate)
    {
        $deferred = new Deferred();

        if ($bitrate > 128000 || $bitrate < 8000) {
            $deferred->reject(new \InvalidArgumentException("{$bitrate} is not a valid option. The bitrate must be between 8,000bpm and 128,000bpm."));

            return $deferred->promise();
        }

        if ($this->speaking) {
            $deferred->reject(new \Exception('Cannot change bitrate while playing.'));

            return $deferred->promise();
        }

        $this->bitrate = $bitrate;

        $deferred->resolve();

        return $deferred->promise();
    }