gst-source: on-demand element creation

Add to GstSource the possibility to create the GStreamer element
when an output port is created, and not directly when the node is
created.

The element is chosen based on the requested format, using
GStreamer typefind as in the GstAutoDetect class.

pinos/modules/gst/gst-source.c

@@ -371,6 +371,7 @@ on_output_port_created (GObject      *source_object,
   PinosNode *node = PINOS_NODE (source_object);
   PinosGstSource *source = PINOS_GST_SOURCE (node);
   PinosGstSourcePrivate *priv = source->priv;
+  GTask *task = user_data;
 
   priv->output = pinos_node_create_port_finish (node, res, NULL);
 
@@ -378,6 +379,12 @@ on_output_port_created (GObject      *source_object,
   g_signal_connect (priv->output, "unlinked", (GCallback) on_unlinked, node);
 
   setup_pipeline (source, NULL);
+
+  if (task) {
+    g_task_return_pointer (task,
+                           priv->output,
+                           (GDestroyNotify) g_object_unref);
+  }
 }
 
 static void
@@ -391,6 +398,7 @@ source_constructed (GObject * object)
 
   G_OBJECT_CLASS (pinos_gst_source_parent_class)->constructed (object);
 
+  if (priv->element) {
     str = gst_caps_to_string (priv->possible_formats);
     possible_formats = g_bytes_new_take (str, strlen (str) + 1);
 
@@ -400,10 +408,11 @@ source_constructed (GObject * object)
                             possible_formats,
                             NULL,
                             NULL,
-                          on_output_port_created,
+                            NULL,
-                          node);
+                            NULL);
     g_bytes_unref (possible_formats);
   }
+}
 
 static void
 source_finalize (GObject * object)
@@ -420,6 +429,113 @@ source_finalize (GObject * object)
   G_OBJECT_CLASS (pinos_gst_source_parent_class)->finalize (object);
 }
 
+static gboolean
+factory_filter (GstPluginFeature * feature, gpointer data)
+{
+  guint rank;
+  const gchar *klass;
+
+  if (!GST_IS_ELEMENT_FACTORY (feature))
+    return FALSE;
+
+  rank = gst_plugin_feature_get_rank (feature);
+  if (rank < 1)
+    return FALSE;
+
+  klass = gst_element_factory_get_metadata (GST_ELEMENT_FACTORY (feature),
+      GST_ELEMENT_METADATA_KLASS);
+  if (g_strcmp0 (klass, "Source/Video") && g_strcmp0 (klass, "Source/Audio"))
+    return FALSE;
+
+  return TRUE;
+}
+
+static GstElement *
+create_best_element (GstCaps *caps)
+{
+  GstElement *element = NULL;
+  GList *list, *item;
+
+  /* get factories from registry */
+  list = gst_registry_feature_filter (gst_registry_get (),
+                                      (GstPluginFeatureFilter) factory_filter,
+                                      FALSE, NULL);
+  list = g_list_sort (list,
+                      (GCompareFunc) gst_plugin_feature_rank_compare_func);
+
+  /* loop through list and try to find factory that best matches caps,
+   * following the pattern from GstAutoDetect */
+  for (item = list; item != NULL; item = item->next) {
+    GstElementFactory *f = GST_ELEMENT_FACTORY (item->data);
+    GstElement *el;
+    GstPad *el_pad;
+    GstCaps *el_caps = NULL;
+    gboolean match = FALSE;
+    GstStateChangeReturn ret;
+
+    if ((el = gst_element_factory_create (f, NULL))) {
+      el_pad = gst_element_get_static_pad (el, "src");
+      el_caps = gst_pad_query_caps (el_pad, NULL);
+      gst_object_unref (el_pad);
+      match = gst_caps_can_intersect (caps, el_caps);
+      gst_caps_unref (el_caps);
+
+      if (!match) {
+        gst_object_unref (el);
+        continue;
+      }
+    }
+
+    ret = gst_element_set_state (el, GST_STATE_READY);
+    if (ret == GST_STATE_CHANGE_SUCCESS) {
+      element = el;
+      g_debug ("element %p selected", element);
+      break;
+    }
+
+    gst_element_set_state (el, GST_STATE_NULL);
+    gst_object_unref (el);
+  }
+
+  return element;
+}
+
+static void
+source_create_port (PinosNode       *node,
+                    PinosDirection   direction,
+                    const gchar     *name,
+                    GBytes          *possible_formats,
+                    PinosProperties *props,
+                    GTask           *task)
+{
+  PinosGstSourcePrivate *priv = PINOS_GST_SOURCE (node)->priv;
+  GTask *source_task;
+
+  if (props == NULL)
+    props = pinos_properties_new (NULL, NULL);
+
+  if (priv->element == NULL) {
+    GstCaps *caps;
+
+    caps = gst_caps_from_string (g_bytes_get_data (possible_formats, NULL));
+    priv->element = create_best_element (caps);
+    gst_caps_unref (caps);
+
+    if (priv->element) {
+      pinos_properties_set (props, "autoconnect", "0");
+    }
+  }
+
+  /* chain up */
+  source_task = g_task_new (node, NULL, on_output_port_created, task);
+  PINOS_NODE_CLASS (pinos_gst_source_parent_class)->create_port (node,
+                                                                 direction,
+                                                                 name,
+                                                                 possible_formats,
+                                                                 props,
+                                                                 source_task);
+}
+
 static void
 pinos_gst_source_class_init (PinosGstSourceClass * klass)
 {
@@ -453,6 +569,7 @@ pinos_gst_source_class_init (PinosGstSourceClass * klass)
                                                        G_PARAM_STATIC_STRINGS));
 
   node_class->set_state = set_state;
+  node_class->create_port = source_create_port;
 }
 
 static void