hook_node_view can't change content
You must declare the field for the DS be able to handle it. In your case:

/**
 * Implements hook_field_extra_fields().
 */
function mymodule_field_extra_fields() {

  $extra['node']['article']['display']['field_video_embed_code'] = array(
    'label' =&gt; t('Custom field embed video.'),
    'description' =&gt; t('Adds a custom field.'),
    'weight' =&gt; 0,
  );
  return $extra;
}