https://wordpress.org/plugins/wp-add-mime-types/

functions.php
 add_filter('upload_mimes','add_custom_mime_types');
 function add_custom_mime_types($mimes){
 return array_merge($mimes,array (
 'ac3' => 'audio/ac3',
 'mpa' => 'audio/MPA',
 'flv' => 'video/x-flv',
 'svg' => 'image/svg+xml'
 ));
 }