diff --git a/gst/videomixer/videomixer2.c b/gst/videomixer/videomixer2.c
index a03cf277d9..78034b3215 100644
--- a/gst/videomixer/videomixer2.c
+++ b/gst/videomixer/videomixer2.c
@@ -1119,6 +1119,22 @@ gst_videomixer2_query_caps (GstPad * pad, GstObject * parent, GstQuery * query)
   return TRUE;
 }
 
+/* FIXME, the duration query should reflect how long you will produce
+ * data, that is the amount of stream time until you will emit EOS.
+ *
+ * For synchronized mixing this is always the max of all the durations
+ * of upstream since we emit EOS when all of them finished.
+ *
+ * We don't do synchronized mixing so this really depends on where the
+ * streams where punched in and what their relative offsets are against
+ * eachother which we can get from the first timestamps we see.
+ *
+ * When we add a new stream (or remove a stream) the duration might
+ * also become invalid again and we need to post a new DURATION
+ * message to notify this fact to the parent.
+ * For now we take the max of all the upstream elements so the simple
+ * cases work at least somewhat.
+ */
 static gboolean
 gst_videomixer2_query_duration (GstVideoMixer2 * mix, GstQuery * query)
 {