baseparse: add getcaps function

Adds a getcaps function to the sink pad to make parsers propagate
downstream caps restrictions to upstream.

The pipeline "audiotestsrc num-buffers=100 ! faac ! aacparse !
"audio/mpeg, version=(int)4, stream-format=(string)adts" ! filesink"
wouldn't work because aacparse wouldn't propagate the adts restriction
upstream to faac.

This patch adds a default getcaps to the sink pad to simply proxy
downstream caps and also adds a 'get_sink_caps' function pointer
to GstBaseParseClass for subclasses that need more refined getcaps.

https://bugzilla.gnome.org/show_bug.cgi?id=661874

libs/gst/base/gstbaseparse.c

@@ -379,6 +379,7 @@ static gboolean gst_base_parse_src_event (GstPad * pad, GstEvent * event);
 static gboolean gst_base_parse_sink_event (GstPad * pad, GstEvent * event);
 static gboolean gst_base_parse_query (GstPad * pad, GstQuery * query);
 static gboolean gst_base_parse_sink_setcaps (GstPad * pad, GstCaps * caps);
+static GstCaps *gst_base_parse_sink_getcaps (GstPad * pad);
 static const GstQueryType *gst_base_parse_get_querytypes (GstPad * pad);
 
 static GstFlowReturn gst_base_parse_chain (GstPad * pad, GstBuffer * buffer);
@@ -512,6 +513,8 @@ gst_base_parse_init (GstBaseParse * parse, GstBaseParseClass * bclass)
       GST_DEBUG_FUNCPTR (gst_base_parse_sink_event));
   gst_pad_set_setcaps_function (parse->sinkpad,
       GST_DEBUG_FUNCPTR (gst_base_parse_sink_setcaps));
+  gst_pad_set_getcaps_function (parse->sinkpad,
+      GST_DEBUG_FUNCPTR (gst_base_parse_sink_getcaps));
   gst_pad_set_chain_function (parse->sinkpad,
       GST_DEBUG_FUNCPTR (gst_base_parse_chain));
   gst_pad_set_activate_function (parse->sinkpad,
@@ -3856,6 +3859,29 @@ gst_base_parse_sink_setcaps (GstPad * pad, GstCaps * caps)
   return res;
 }
 
+static GstCaps *
+gst_base_parse_sink_getcaps (GstPad * pad)
+{
+  GstBaseParse *parse;
+  GstBaseParseClass *klass;
+  GstCaps *caps;
+
+  parse = GST_BASE_PARSE (gst_pad_get_parent (pad));
+  klass = GST_BASE_PARSE_GET_CLASS (parse);
+  g_assert (pad == GST_BASE_PARSE_SINK_PAD (parse));
+
+  if (klass->get_sink_caps)
+    caps = klass->get_sink_caps (parse);
+  else
+    caps = gst_pad_proxy_getcaps (pad);
+  gst_object_unref (parse);
+
+  GST_LOG_OBJECT (parse, "sink getcaps returning caps %" GST_PTR_FORMAT, caps);
+
+  return caps;
+
+}
+
 static void
 gst_base_parse_set_index (GstElement * element, GstIndex * index)
 {

libs/gst/base/gstbaseparse.h

@@ -191,6 +191,7 @@ struct _GstBaseParse {
  *                  Called when the element stops processing.
  *                  Allows closing external resources.
  * @set_sink_caps:  allows the subclass to be notified of the actual caps set.
+ * @get_sink_caps:  allows the subclass to do its own sink get caps if needed.
  * @check_valid_frame:  Check if the given piece of data contains a valid
  *                      frame.
  * @parse_frame:    Parse the already checked frame. Subclass need to
@@ -252,8 +253,10 @@ struct _GstBaseParseClass {
   gboolean      (*src_event)          (GstBaseParse * parse,
                                        GstEvent     * event);
 
+  GstCaps *     (*get_sink_caps)      (GstBaseParse * parse);
+
   /*< private >*/
-  gpointer       _gst_reserved[GST_PADDING_LARGE];
+  gpointer       _gst_reserved[GST_PADDING_LARGE - 1];
 };
 
 GType           gst_base_parse_get_type (void);