function get_file_extension($file) {

        return array_pop(explode('.',$file));
    }

    function get_mimetype($value='') {

        $ct['htm'] = 'text/html';
        $ct['html'] = 'text/html';
        $ct['txt'] = 'text/plain';
        $ct['asc'] = 'text/plain';
        $ct['bmp'] = 'image/bmp';
        $ct['gif'] = 'image/gif';
        $ct['jpeg'] = 'image/jpeg';
        $ct['jpg'] = 'image/jpeg';
        $ct['jpe'] = 'image/jpeg';
        $ct['png'] = 'image/png';
        $ct['ico'] = 'image/vnd.microsoft.icon';
        $ct['mpeg'] = 'video/mpeg';
        $ct['mpg'] = 'video/mpeg';
        $ct['mpe'] = 'video/mpeg';
        $ct['qt'] = 'video/quicktime';
        $ct['mov'] = 'video/quicktime';
        $ct['avi']  = 'video/x-msvideo';
        $ct['wmv'] = 'video/x-ms-wmv';
        $ct['mp2'] = 'audio/mpeg';
        $ct['mp3'] = 'audio/mpeg';
        $ct['rm'] = 'audio/x-pn-realaudio';
        $ct['ram'] = 'audio/x-pn-realaudio';
        $ct['rpm'] = 'audio/x-pn-realaudio-plugin';
        $ct['ra'] = 'audio/x-realaudio';
        $ct['wav'] = 'audio/x-wav';
        $ct['css'] = 'text/css';
        $ct['zip'] = 'application/zip';
        $ct['pdf'] = 'application/pdf';
        $ct['doc'] = 'application/msword';
        $ct['bin'] = 'application/octet-stream';
        $ct['exe'] = 'application/octet-stream';
        $ct['class']= 'application/octet-stream';
        $ct['dll'] = 'application/octet-stream';
        $ct['xls'] = 'application/vnd.ms-excel';
        $ct['ppt'] = 'application/vnd.ms-powerpoint';
        $ct['wbxml']= 'application/vnd.wap.wbxml';
        $ct['wmlc'] = 'application/vnd.wap.wmlc';
        $ct['wmlsc']= 'application/vnd.wap.wmlscriptc';
        $ct['dvi'] = 'application/x-dvi';
        $ct['spl'] = 'application/x-futuresplash';
        $ct['gtar'] = 'application/x-gtar';
        $ct['gzip'] = 'application/x-gzip';
        $ct['js'] = 'application/x-javascript';
        $ct['swf'] = 'application/x-shockwave-flash';
        $ct['tar'] = 'application/x-tar';
        $ct['xhtml']= 'application/xhtml+xml';
        $ct['au'] = 'audio/basic';
        $ct['snd'] = 'audio/basic';
        $ct['midi'] = 'audio/midi';
        $ct['mid'] = 'audio/midi';
        $ct['m3u'] = 'audio/x-mpegurl';
        $ct['tiff'] = 'image/tiff';
        $ct['tif'] = 'image/tiff';
        $ct['rtf'] = 'text/rtf';
        $ct['wml'] = 'text/vnd.wap.wml';
        $ct['wmls'] = 'text/vnd.wap.wmlscript';
        $ct['xsl'] = 'text/xml';
        $ct['xml'] = 'text/xml';

        $extension = get_file_extension($value);

        if (!$type = $ct[strtolower($extension)]) {

            $type = 'text/html';
        }

        return $type;
    }

You only use the filename as $value
for get_mimetype().

get file mime-type

file

PHP