A MODx plugin to hook into the 'fileadd' event of the file-upload-dialog and render a window with a form to fill out. Please use carefully!

file-upload-dialog-hook

<?php
$event = $modx->event->name;
switch($event) {
  case 'OnManagerPageInit':
    $id = 'ext-comp-1107';

    $js =<<<JS
      <script type="text/javascript">
      function find_dialog() {
        Ext.onReady(function() {

          // var dialog = Ext.getCmp('modx-upload-window');
          // console.log(dialog);

          var updialog = Ext.getCmp('$id');
          // console.log(updialog);
          if(updialog)
            window.clearInterval(interval);
          if(!updialog)
            return;

          function add_window(filename, path) {

            var medialib_form = new Ext.FormPanel({
                url: MODx.config.base_url + 'assets/save-form.php',
                frame:true,
                defaultType: 'textfield',
                items: [{
                    xtype: 'hidden',
                    name: 'path',
                    value: path,
                  },{
                    xtype: 'hidden',
                    name: 'filename',
                    value: filename,
                  },{
                    fieldLabel: 'Titel',
                    name: 'title',
                    anchor: '100%',
                    allowBlank:false
                  },{
                    xtype: 'textarea',
                    fieldLabel: 'Copyright',
                    name: 'copyright',
                    anchor: '100%',
                    allowBlank:false
                  },{
                    xtype: 'textarea',
                    fieldLabel: 'Beschreibung',
                    name: 'description',
                    anchor: '100%',
                  }
                ],

                buttons: [{
                    text: 'Speichern',
                    handler: function(button, e){
                        // medialib_form.getForm().submit();
                        var form = medialib_form.getForm();
                        if (form.isValid()) {
                            form.submit({
                                success: function(form, action) {
                                   win.close();
                                },
                                failure: function(form, action) {
                                    Ext.Msg.alert('Fehler', action.result ? action.result.message : 'Keine Antwort');
                                }
                            });
                        } else {
                            Ext.Msg.alert( "Fehler!", "Bitte füllen Sie das Formular korrekt aus!" );
                        }
                    }
                },{
                    text: 'Abbrechen',
                    handler: function(button, e) {
                      win.close();
                    }
                }]
            });

            var win = new Ext.Window({
              id: 'my_window'
              , title : "Medienbibliothek"
              , width : 500
              , height: 500
              , layout: "fit"
              ,items: medialib_form
            });
            win.show();
          }

          Ext.getCmp('$id').on('fileadd', function(dialog, filename) {
            var ext = filename.split('.').pop();
            var allowed = ['jpg', 'jpeg', 'gif', 'png'];
            if(allowed.indexOf(ext) == -1)
              return;
            add_window( filename, dialog.base_params.path);
          });

        });
      }

      var interval = window.setInterval(function(){find_dialog();}, 1000);
    </script>
JS;
    $modx->regClientStartupScript($js);
  break;
}
return;