taginject: Modify existing tag events of the selected scope

Not doing so would mean that tags would be overidden by any tag events sent by
upstream. Also only send a tag event directly if upstream never sent one.

By default use GST_TAG_MERGE_REPLACE to override tags that exist in both the
upstream event and this element with the ones from this element, but provide a
new "merge-mode" property to adjust the behaviour.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7145>

subprojects/gst-plugins-good/docs/gst_plugins_cache.json

@@ -4935,6 +4935,18 @@
                     }
                 },
                 "properties": {
+                    "merge-mode": {
+                        "blurb": "Merge mode to merge tags from this element with upstream tags",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "replace (2)",
+                        "mutable": "null",
+                        "readable": true,
+                        "type": "GstTagMergeMode",
+                        "writable": true
+                    },
                     "scope": {
                         "blurb": "Scope of tags to inject (stream | global)",
                         "conditionally-available": false,

subprojects/gst-plugins-good/gst/debugutils/gsttaginject.c

@@ -63,7 +63,8 @@ GST_DEBUG_CATEGORY_STATIC (gst_tag_inject_debug);
 enum
 {
   PROP_TAGS = 1,
-  PROP_SCOPE
+  PROP_SCOPE,
+  PROP_MERGE_MODE
 };
 
 
@@ -80,6 +81,8 @@ static void gst_tag_inject_get_property (GObject * object, guint prop_id,
 
 static GstFlowReturn gst_tag_inject_transform_ip (GstBaseTransform * trans,
     GstBuffer * buf);
+static gboolean gst_tag_inject_sink_event (GstBaseTransform * trans,
+    GstEvent * event);
 static gboolean gst_tag_inject_start (GstBaseTransform * trans);
 
 
@@ -131,6 +134,19 @@ gst_tag_inject_class_init (GstTagInjectClass * klass)
           GST_TYPE_TAG_SCOPE, GST_TAG_SCOPE_STREAM,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
+  /**
+   * taginject:merge-mode:
+   *
+   * Merge mode to merge tags from this element with upstream tags.
+   *
+   * Since: 1.26
+   **/
+  g_object_class_install_property (gobject_class, PROP_MERGE_MODE,
+      g_param_spec_enum ("merge-mode", "Merge Mode",
+          "Merge mode to merge tags from this element with upstream tags",
+          GST_TYPE_TAG_MERGE_MODE, GST_TAG_MERGE_REPLACE,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
+
   gobject_class->finalize = gst_tag_inject_finalize;
 
   gst_element_class_set_static_metadata (gstelement_class,
@@ -141,6 +157,8 @@ gst_tag_inject_class_init (GstTagInjectClass * klass)
 
   gstbasetrans_class->transform_ip =
       GST_DEBUG_FUNCPTR (gst_tag_inject_transform_ip);
+  gstbasetrans_class->sink_event =
+      GST_DEBUG_FUNCPTR (gst_tag_inject_sink_event);
 
   gstbasetrans_class->start = GST_DEBUG_FUNCPTR (gst_tag_inject_start);
 }
@@ -154,6 +172,7 @@ gst_tag_inject_init (GstTagInject * self)
 
   self->tags = NULL;
   self->tags_scope = GST_TAG_SCOPE_STREAM;
+  self->merge_mode = GST_TAG_MERGE_REPLACE;
 }
 
 static GstFlowReturn
@@ -174,6 +193,36 @@ gst_tag_inject_transform_ip (GstBaseTransform * trans, GstBuffer * buf)
   return GST_FLOW_OK;
 }
 
+static gboolean
+gst_tag_inject_sink_event (GstBaseTransform * trans, GstEvent * event)
+{
+  GstTagInject *self = GST_TAG_INJECT (trans);
+
+  switch (GST_EVENT_TYPE (event)) {
+    case GST_EVENT_TAG:{
+      GstTagList *tags;
+
+      gst_event_parse_tag (event, &tags);
+      if (gst_tag_list_get_scope (tags) == self->tags_scope) {
+        GstTagList *new_tags;
+        guint32 seqnum = gst_event_get_seqnum (event);
+
+        new_tags = gst_tag_list_merge (tags, self->tags, self->merge_mode);
+        gst_tag_list_set_scope (new_tags, self->tags_scope);
+        gst_event_unref (event);
+        event = gst_event_new_tag (new_tags);
+        gst_event_set_seqnum (event, seqnum);
+
+        self->tags_sent = TRUE;
+      }
+    }
+    default:
+      break;
+  }
+
+  return GST_BASE_TRANSFORM_CLASS (parent_class)->sink_event (trans, event);
+}
+
 static void
 gst_tag_inject_set_property (GObject * object, guint prop_id,
     const GValue * value, GParamSpec * pspec)
@@ -200,6 +249,9 @@ gst_tag_inject_set_property (GObject * object, guint prop_id,
       if (self->tags)
         gst_tag_list_set_scope (self->tags, self->tags_scope);
       break;
+    case PROP_MERGE_MODE:
+      self->merge_mode = g_value_get_enum (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -220,6 +272,9 @@ gst_tag_inject_get_property (GObject * object, guint prop_id, GValue * value,
     case PROP_SCOPE:
       g_value_set_enum (value, self->tags_scope);
       break;
+    case PROP_MERGE_MODE:
+      g_value_set_enum (value, self->merge_mode);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;

subprojects/gst-plugins-good/gst/debugutils/gsttaginject.h

@@ -54,6 +54,7 @@ struct _GstTagInject
   GstTagList *tags;
   gboolean tags_sent;
   GstTagScope tags_scope;
+  GstTagMergeMode merge_mode;
 };
 
 struct _GstTagInjectClass