PHP File attribute for avi files

ok, heres the cryptic clue from some PHP script.....

['image'][] = 'gif';
['image'][] = 'jpg';
['image'][] = 'png';
['text'][] = 'txt';

['exec'][] = 'php';
['exec'][] = 'asp';
['exec'][] = 'cgi';

['package'][] = 'zip';
['package'][] = 'exe';
['package'][] = 'mp3';

['????'][] = 'avi';
what's the correct attribute for avi files that i need to put in the first box?