I don’t think it’s documented in Codex but quick search in code shows that you can query by mime type. For jpeg images that would be something like:
$posts = get_posts( array(
'post_type' => 'attachment',
'post_status' => 'any',
'post_mime_type' => 'image/jpeg',
) );
Not sure what types WP uses for files you need, don’t have such in test stack to check.