baseparse: Make sure to not create an invalid event order when generating the default CAPS event because of a GAP event

There must be a SEGMENT event before the GAP event, and SEGMENT events must
come after any CAPS event. We however did not produce any CAPS yet, so we need
to ensure to insert the CAPS event before the SEGMENT event into the pending
events list.

https://bugzilla.gnome.org/show_bug.cgi?id=766970

libs/gst/base/gstbaseparse.c

@@ -1405,11 +1405,32 @@ gst_base_parse_sink_event_default (GstBaseParse * parse, GstEvent * event)
       if (!gst_pad_has_current_caps (GST_BASE_PARSE_SRC_PAD (parse))) {
         GstCaps *default_caps = NULL;
         if ((default_caps = gst_base_parse_negotiate_default_caps (parse))) {
+          GList *l;
+          GstEvent *caps_event = gst_event_new_caps (default_caps);
+
           GST_DEBUG_OBJECT (parse,
               "Store caps event to pending list for initial pre-rolling");
-          parse->priv->pending_events =
+
-              g_list_prepend (parse->priv->pending_events,
+          /* Events are in decreasing order. Go down the list until we
-              gst_event_new_caps (default_caps));
+           * find the first pre-CAPS event and insert our CAPS event there.
+           *
+           * There should be a SEGMENT event already, which is > CAPS */
+          for (l = parse->priv->pending_events; l; l = l->next) {
+            GstEvent *e = l->data;
+
+            if (GST_EVENT_TYPE (e) < GST_EVENT_CAPS) {
+              parse->priv->pending_events =
+                  g_list_insert_before (parse->priv->pending_events, l,
+                  caps_event);
+              break;
+            }
+          }
+          /* No pending event that is < CAPS, so we have to add it at the very
+           * end of the list */
+          if (!l) {
+            parse->priv->pending_events =
+                g_list_append (parse->priv->pending_events, caps_event);
+          }
           gst_caps_unref (default_caps);
         } else {
           gst_event_unref (event);