urisourcebin: Aggregate collections from multiple parsebin

In the case where multiple parsebin are present (ex: from rtsp sources), we want
to aggregate the collections provided by the different parsebin and expose a
single "unified" collection.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7716>

subprojects/gst-plugins-base/gst/playback/gsturisourcebin.c

@@ -122,6 +122,9 @@ struct _ChildSrcPadInfo
   /* use_queue2: TRUE if the contents should be buffered through a queue2
    * element */
   gboolean use_queue2;
+
+  /* Current StreamCollection */
+  GstStreamCollection *collection;
 };
 
 /* Output Slot:
@@ -194,6 +197,9 @@ struct _GstURISourceBin
   gint last_buffering_pct;      /* Avoid sending buffering over and over */
   GMutex buffering_lock;
   GMutex buffering_post_lock;
+
+  /* Current output collection (if provided by internal elements) */
+  GstStreamCollection *collection;
 };
 
 struct _GstURISourceBinClass
@@ -565,6 +571,7 @@ gst_uri_source_bin_finalize (GObject * obj)
   g_mutex_clear (&urisrc->buffering_post_lock);
   g_free (urisrc->uri);
   g_free (urisrc->download_dir);
+  gst_object_replace ((GstObject **) & urisrc->collection, NULL);
 
   G_OBJECT_CLASS (parent_class)->finalize (obj);
 }
@@ -786,6 +793,8 @@ free_child_src_pad_info (ChildSrcPadInfo * info, GstURISourceBin * urisrc)
     gst_bin_remove (GST_BIN_CAST (urisrc), info->pre_parse_queue);
   }
 
+  gst_object_replace ((GstObject **) & info->collection, NULL);
+
   g_free (info);
 }
 
@@ -2909,8 +2918,80 @@ handle_parsebin_collection (ChildSrcPadInfo * info,
 
   g_list_free (unused_slots);
   g_list_free (streams);
+
+  /* Store the collection */
+  gst_object_replace ((GstObject **) & info->collection,
+      (GstObject *) collection);
 }
 
+/* uri_source_bin_aggregate_collection:
+ *
+ * Go over the collections provided by the various parsebin (via
+ * ChildSrcPadInfo) and provide a unified collection.
+ *
+ * If there are more than one collection and they are different, a new
+ * aggregated collection will be returned.
+ *
+ * In all cases, the collection will be stored as the uri source bin main
+ * collection.
+ *
+ * Return: (transfer full): The collection, or %NULL.
+ */
+static GstStreamCollection *
+uri_source_bin_aggregate_collection (GstURISourceBin * urisrc)
+{
+  GList *iter;
+  GList *streams = NULL;
+  gboolean collections_need_merging = FALSE;
+  GstStreamCollection *res = NULL;
+
+  for (iter = urisrc->src_infos; iter; iter = iter->next) {
+    ChildSrcPadInfo *info = iter->data;
+
+    GST_DEBUG_OBJECT (info->demuxer, "collection %" GST_PTR_FORMAT,
+        info->collection);
+    if (res && info->collection && info->collection != res) {
+      collections_need_merging = TRUE;
+      break;
+    }
+
+    if (info->collection)
+      res = info->collection;
+  }
+
+  if (!collections_need_merging) {
+    GST_DEBUG_OBJECT (urisrc, "No need to aggregate");
+    goto store_exit;
+  }
+
+  res = gst_stream_collection_new ("urisourcebin");
+  for (iter = urisrc->src_infos; iter; iter = iter->next) {
+    ChildSrcPadInfo *info = iter->data;
+    if (info->collection) {
+      guint i, len;
+      len = gst_stream_collection_get_size (info->collection);
+      for (i = 0; i < len; i++) {
+        GstStream *stream =
+            gst_stream_collection_get_stream (info->collection, i);
+        if (!g_list_find (streams, stream)) {
+          streams = g_list_append (streams, stream);
+        }
+      }
+    }
+  }
+
+  for (iter = streams; iter; iter = iter->next) {
+    GstStream *stream = iter->data;
+    gst_stream_collection_add_stream (res, gst_object_ref (stream));
+  }
+  if (streams)
+    g_list_free (streams);
+
+store_exit:
+  gst_object_replace ((GstObject **) & urisrc->collection, (GstObject *) res);
+  GST_DEBUG_OBJECT (urisrc, "Aggregated collection %" GST_PTR_FORMAT, res);
+  return res ? gst_object_ref (res) : NULL;
+}
 
 static void
 handle_message (GstBin * bin, GstMessage * msg)
@@ -2948,16 +3029,20 @@ handle_message (GstBin * bin, GstMessage * msg)
         if (info->demuxer_is_parsebin) {
           GstStreamCollection *collection = NULL;
           gst_message_parse_stream_collection (msg, &collection);
+          GST_DEBUG_OBJECT (bin, "Seen collection %" GST_PTR_FORMAT,
+              collection);
           /* Check if some output slots can/could be re-used with this new collection */
           if (collection) {
+            GstStreamCollection *aggregated = NULL;
             handle_parsebin_collection (info, collection);
-            gst_object_unref (collection);
+            aggregated = uri_source_bin_aggregate_collection (urisrc);
-          }
+            if (aggregated != collection) {
-          if (g_list_length (urisrc->src_infos) > 1) {
-            GST_DEBUG_OBJECT (bin,
-                "Dropping stream-collection, multiple parsebins present");
               gst_message_unref (msg);
-            msg = NULL;
+              msg =
+                  gst_message_new_stream_collection ((GstObject *) urisrc,
+                  aggregated);
+            }
+            gst_object_unref (collection);
           }
         }
       } else if (GST_MESSAGE_SRC (msg) != (GstObject *) urisrc->source) {