protected function convert($vObj)
    {
        $json = false;
        $convertVersion = null;
        $forceInput = null;

        switch ($this->format) {
            case 'json':
                $json = true;
                if ('VCARD' === $vObj->name) {
                    $convertVersion = Document::VCARD40;
                }
                break;
            case 'jcard':
                $json = true;
                $forceInput = 'VCARD';
                $convertVersion = Document::VCARD40;
                break;
            case 'jcal':
                $json = true;
                $forceInput = 'VCALENDAR';
                break;
            case 'mimedir':
            case 'icalendar':
            case 'icalendar20':
            case 'vcard':
                break;
            case 'vcard21':
                $convertVersion = Document::VCARD21;
                break;
            case 'vcard30':
                $convertVersion = Document::VCARD30;
                break;
            case 'vcard40':
                $convertVersion = Document::VCARD40;
                break;
        }

        if ($forceInput && $vObj->name !== $forceInput) {
            throw new \Exception('You cannot convert a '.strtolower($vObj->name).' to '.$this->format);
        }
        if ($convertVersion) {
            $vObj = $vObj->convert($convertVersion);
        }
        if ($json) {
            $jsonOptions = 0;
            if ($this->pretty) {
                $jsonOptions = JSON_PRETTY_PRINT;
            }
            fwrite($this->stdout, json_encode($vObj->jsonSerialize(), $jsonOptions));
        } else {
            fwrite($this->stdout, $vObj->serialize());
        }

        return 0;
    }