8 0 h g

cd wp-content/plugins

mkdir my-add-upload-ext

cd  my-add-upload-ext

vim my-add-upload-ext.php

<?php
/*
Plugin Name: add-upload-ext for my site web
Description: Permet d'ajouter des extensions de fichier pour l'upload dans la Médiathèque
*/
/* Functions begin */

function my_myme_types($mime_types){
    $mime_types['svg'] = 'image/svg+xml'; //Adding svg files
    $mime_types['psd'] = 'image/vnd.adobe.photoshop'; //Adding photoshop files
    $mime_types['ogv'] = 'video/ogg'; //Adding ogg video files
    return $mime_types;
}
add_filter('upload_mimes', 'my_myme_types', 1, 1);

/* Functions end */
?>

Puis activer le plugin dans les Extension de WordPress, et ça marche

Source : http://www.wpbeginner.com/beginners-guide/what-why-and-how-tos-of-creating-a-site-specific-wordpress-plugin | http://www.mime-type.net/