code: function (e) {
                  var that = $(this).data('blueimp-fileupload') ||
                          $(this).data('fileupload');
                  that._resetFinishedDeferreds();
                  that._transition($(this).find('.fileupload-progress')).done(
                      function () {
                          that._trigger('started', e);
                      }
                  );
              }
docs: Callback for uploads start, equivalent to the global ajaxStart event: