valve: Add modes to forward sticky events when dropping and to convert buffers into gap events

Fixes https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/587
Fixes https://gitlab.freedesktop.org/gstreamer/gstreamer/-/issues/84

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/594>

docs/plugins/gst_plugins_cache.json

@@ -2445,6 +2445,18 @@
                         "readable": true,
                         "type": "gboolean",
                         "writable": true
+                    },
+                    "drop-mode": {
+                        "blurb": "The drop mode to use",
+                        "conditionally-available": false,
+                        "construct": false,
+                        "construct-only": false,
+                        "controllable": false,
+                        "default": "drop-all (0)",
+                        "mutable": "ready",
+                        "readable": true,
+                        "type": "GstValveDropMode",
+                        "writable": true
                     }
                 },
                 "rank": "none"
@@ -2796,6 +2808,26 @@
                         "value": "1"
                     }
                 ]
+            },
+            "GstValveDropMode": {
+                "kind": "enum",
+                "values": [
+                    {
+                        "desc": "Drop all buffers and events",
+                        "name": "drop-all",
+                        "value": "0"
+                    },
+                    {
+                        "desc": "Drop all buffers but forward sticky events",
+                        "name": "forward-sticky-events",
+                        "value": "1"
+                    },
+                    {
+                        "desc": "Convert all dropped buffers into gap events and forward sticky events",
+                        "name": "transform-to-gap",
+                        "value": "2"
+                    }
+                ]
             }
         },
         "package": "GStreamer",

plugins/elements/gstvalve.c

@@ -43,6 +43,27 @@
 GST_DEBUG_CATEGORY_STATIC (valve_debug);
 #define GST_CAT_DEFAULT (valve_debug)
 
+#define GST_TYPE_VALVE_DROP_MODE (gst_valve_drop_mode_get_type ())
+static GType
+gst_valve_drop_mode_get_type (void)
+{
+  static GType drop_mode_type = 0;
+  static const GEnumValue drop_mode[] = {
+    {GST_VALVE_DROP_MODE_DROP_ALL, "Drop all buffers and events", "drop-all"},
+    {GST_VALVE_DROP_MODE_FORWARD_STICKY_EVENTS,
+        "Drop all buffers but forward sticky events", "forward-sticky-events"},
+    {GST_VALVE_DROP_MODE_TRANSFORM_TO_GAP,
+          "Convert all dropped buffers into gap events and forward sticky events",
+        "transform-to-gap"},
+    {0, NULL, NULL},
+  };
+
+  if (!drop_mode_type) {
+    drop_mode_type = g_enum_register_static ("GstValveDropMode", drop_mode);
+  }
+  return drop_mode_type;
+}
+
 static GstStaticPadTemplate sinktemplate = GST_STATIC_PAD_TEMPLATE ("sink",
     GST_PAD_SINK,
     GST_PAD_ALWAYS,
@@ -56,10 +77,12 @@ static GstStaticPadTemplate srctemplate = GST_STATIC_PAD_TEMPLATE ("src",
 enum
 {
   PROP_0,
-  PROP_DROP
+  PROP_DROP,
+  PROP_DROP_MODE
 };
 
 #define DEFAULT_DROP FALSE
+#define DEFAULT_DROP_MODE GST_VALVE_DROP_MODE_DROP_ALL
 
 static void gst_valve_set_property (GObject * object,
     guint prop_id, const GValue * value, GParamSpec * pspec);
@@ -96,18 +119,35 @@ gst_valve_class_init (GstValveClass * klass)
           DEFAULT_DROP, G_PARAM_READWRITE | GST_PARAM_MUTABLE_PLAYING |
           G_PARAM_STATIC_STRINGS));
 
+  /**
+   * GstValve:drop-mode
+   *
+   * Drop mode to use. By default all buffers and events are dropped.
+   *
+   * Since: 1.20
+   */
+  g_object_class_install_property (gobject_class, PROP_DROP_MODE,
+      g_param_spec_enum ("drop-mode", "Drop mode",
+          "The drop mode to use", GST_TYPE_VALVE_DROP_MODE,
+          DEFAULT_DROP_MODE,
+          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS |
+          GST_PARAM_MUTABLE_READY));
+
   gst_element_class_add_static_pad_template (gstelement_class, &srctemplate);
   gst_element_class_add_static_pad_template (gstelement_class, &sinktemplate);
 
   gst_element_class_set_static_metadata (gstelement_class, "Valve element",
       "Filter", "Drops buffers and events or lets them through",
       "Olivier Crete <olivier.crete@collabora.co.uk>");
+
+  gst_type_mark_as_plugin_api (GST_TYPE_VALVE_DROP_MODE, 0);
 }
 
 static void
 gst_valve_init (GstValve * valve)
 {
   valve->drop = FALSE;
+  valve->drop_mode = DEFAULT_DROP;
   valve->discont = FALSE;
 
   valve->srcpad = gst_pad_new_from_static_template (&srctemplate, "src");
@@ -140,6 +180,9 @@ gst_valve_set_property (GObject * object,
       g_atomic_int_set (&valve->drop, g_value_get_boolean (value));
       gst_pad_push_event (valve->sinkpad, gst_event_new_reconfigure ());
       break;
+    case PROP_DROP_MODE:
+      valve->drop_mode = g_value_get_enum (value);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -156,6 +199,9 @@ gst_valve_get_property (GObject * object,
     case PROP_DROP:
       g_value_set_boolean (value, g_atomic_int_get (&valve->drop));
       break;
+    case PROP_DROP_MODE:
+      g_value_set_enum (value, valve->drop_mode);
+      break;
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
       break;
@@ -188,6 +234,11 @@ gst_valve_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
   GstFlowReturn ret = GST_FLOW_OK;
 
   if (g_atomic_int_get (&valve->drop)) {
+    if (valve->drop_mode == GST_VALVE_DROP_MODE_TRANSFORM_TO_GAP) {
+      GstEvent *ev = gst_event_new_gap (GST_BUFFER_PTS (buffer),
+          GST_BUFFER_DURATION (buffer));
+      gst_pad_push_event (valve->srcpad, ev);
+    }
     gst_buffer_unref (buffer);
     valve->discont = TRUE;
   } else {
@@ -213,17 +264,37 @@ gst_valve_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
   return ret;
 }
 
+static inline gboolean
+gst_valve_event_needs_dropping (GstValve * valve, GstEvent * event)
+{
+  if (!g_atomic_int_get (&valve->drop))
+    return FALSE;
+
+  switch (valve->drop_mode) {
+    case GST_VALVE_DROP_MODE_DROP_ALL:
+      return TRUE;
+    case GST_VALVE_DROP_MODE_FORWARD_STICKY_EVENTS:
+      return !GST_EVENT_IS_STICKY (event);
+    case GST_VALVE_DROP_MODE_TRANSFORM_TO_GAP:
+      return (!GST_EVENT_IS_STICKY (event) &&
+          GST_EVENT_TYPE (event) != GST_EVENT_GAP);
+    default:
+      g_assert_not_reached ();
+      break;
+  }
+}
 
 static gboolean
 gst_valve_sink_event (GstPad * pad, GstObject * parent, GstEvent * event)
 {
-  GstValve *valve;
+  GstValve *valve = GST_VALVE (parent);
+  gboolean needs_dropping = gst_valve_event_needs_dropping (valve, event);
   gboolean is_sticky = GST_EVENT_IS_STICKY (event);
   gboolean ret = TRUE;
 
   valve = GST_VALVE (parent);
 
-  if (g_atomic_int_get (&valve->drop)) {
+  if (needs_dropping) {
     valve->need_repush_sticky |= is_sticky;
     gst_event_unref (event);
   } else {
@@ -233,9 +304,10 @@ gst_valve_sink_event (GstPad * pad, GstObject * parent, GstEvent * event)
   }
 
   /* Ignore errors if "drop" was changed while the thread was blocked
-   * downwards.
+   * downwards, or if we're dropping but forwarding sticky events nonetheless.
    */
   if (g_atomic_int_get (&valve->drop)) {
+    if (valve->drop_mode == GST_VALVE_DROP_MODE_DROP_ALL)
       valve->need_repush_sticky |= is_sticky;
     ret = TRUE;
   }

plugins/elements/gstvalve.h

@@ -44,6 +44,23 @@ G_BEGIN_DECLS
 typedef struct _GstValve GstValve;
 typedef struct _GstValveClass GstValveClass;
 
+/**
+ * GstValveDropMode:
+ * @GST_VALVE_DROP_MODE_DROP_ALL: Drop all buffers, buffer lists and events.
+ * @GST_VALVE_DROP_MODE_FORWARD_STICKY_EVENTS: Drop all buffers, buffer lists
+ *     and non-sticky events but forward sticky events.
+ * @GST_VALVE_DROP_MODE_TRANSFORM_TO_GAP: Drop all buffers, buffer lists and
+ *     non-sticky events but forward sticky events and forward GAP events for each
+ *     dropped buffer.
+ *
+ * Since: 1.20
+ */
+typedef enum {
+  GST_VALVE_DROP_MODE_DROP_ALL,
+  GST_VALVE_DROP_MODE_FORWARD_STICKY_EVENTS,
+  GST_VALVE_DROP_MODE_TRANSFORM_TO_GAP,
+} GstValveDropMode;
+
 /**
  * GstValve:
  *
@@ -57,6 +74,8 @@ struct _GstValve
   /* atomic boolean */
   volatile gint drop;
 
+  GstValveDropMode drop_mode;
+
   /* Protected by the stream lock */
   gboolean discont;
   gboolean need_repush_sticky;