buffer: add gst_buffer_get_n_meta() convenience function

Counts how many metas there are for a certain api type.

https://bugzilla.gnome.org/show_bug.cgi?id=791918

docs/gst/gstreamer-sections.txt

@@ -253,6 +253,7 @@ gst_buffer_append
 gst_buffer_append_region
 
 gst_buffer_get_meta
+gst_buffer_get_n_meta
 gst_buffer_add_meta
 gst_buffer_remove_meta
 gst_buffer_iterate_meta

gst/gstbuffer.c

@@ -2139,6 +2139,28 @@ gst_buffer_get_meta (GstBuffer * buffer, GType api)
   return result;
 }
 
+/**
+ * gst_buffer_get_n_meta:
+ * @buffer: a #GstBuffer
+ * @api_type: the #GType of an API
+ *
+ * Returns: number of metas of type @api_type on @buffer.
+ *
+ * Since: 1.14
+ */
+guint
+gst_buffer_get_n_meta (GstBuffer * buffer, GType api_type)
+{
+  gpointer state = NULL;
+  GstMeta *meta;
+  guint n = 0;
+
+  while ((meta = gst_buffer_iterate_meta_filtered (buffer, &state, api_type)))
+    ++n;
+
+  return n;
+}
+
 /**
  * gst_buffer_add_meta:
  * @buffer: a #GstBuffer

gst/gstbuffer.h

@@ -612,6 +612,9 @@ typedef gboolean (*GstBufferForeachMetaFunc)    (GstBuffer *buffer, GstMeta **me
 GST_EXPORT
 GstMeta *       gst_buffer_get_meta             (GstBuffer *buffer, GType api);
 
+GST_EXPORT
+guint           gst_buffer_get_n_meta           (GstBuffer *buffer, GType api);
+
 GST_EXPORT
 GstMeta *       gst_buffer_add_meta             (GstBuffer *buffer, const GstMetaInfo *info,
                                                  gpointer params);

win32/common/libgstreamer.def

@@ -136,6 +136,7 @@ EXPORTS
 	gst_buffer_get_memory
 	gst_buffer_get_memory_range
 	gst_buffer_get_meta
+	gst_buffer_get_n_meta
 	gst_buffer_get_reference_timestamp_meta
 	gst_buffer_get_size
 	gst_buffer_get_sizes