tag: add musical-key tag

https://bugzilla.gnome.org/show_bug.cgi?id=705999

gst-libs/gst/tag/tag.h

@@ -81,6 +81,21 @@ G_BEGIN_DECLS
  * Annodex CMML clip element tag
  */
 #define GST_TAG_CMML_CLIP "cmml-clip"
+/**
+ * GST_TAG_MUSICAL_KEY:
+ *
+ * Musical key in which the sound starts. It is represented as a string
+ * with a maximum length of three characters. The ground keys are
+ * represented with "A","B","C","D","E", "F" and "G" and halfkeys
+ * represented with "b" and "#". Minor is represented as "m" (e.g. "Dbm").
+ * Off key is represented with an "o" only.
+ * This notation might be extended in the future to support non-minor/major
+ * keys.
+ *
+ * Since: 1.2
+ */
+#define GST_TAG_MUSICAL_KEY                   "musical-key"
+
 
 /* CDDA tags */
 

gst-libs/gst/tag/tags.c

@@ -194,6 +194,10 @@ gst_tag_register_tags_internal (gpointer unused)
       GST_TYPE_BUFFER, _("ID3v2 frame"), _("unparsed id3v2 tag frame"),
       gst_tag_merge_use_first);
 
+  gst_tag_register_static (GST_TAG_MUSICAL_KEY, GST_TAG_FLAG_META,
+      G_TYPE_STRING, _("musical-key"), _("Initial key in which the "
+          "sound starts"), gst_tag_merge_use_first);
+
   return NULL;
 }