videodecoder: expose getcaps virtual function

Allows subclasses to do custom caps query replies.

Also exposes the standard caps query handler so subclasses can just
extend on top of it instead of reimplementing the caps query proxying.

https://bugzilla.gnome.org/show_bug.cgi?id=741263

gst-libs/gst/video/gstvideodecoder.c

@@ -1578,6 +1578,47 @@ gst_video_decoder_src_query (GstPad * pad, GstObject * parent, GstQuery * query)
   return ret;
 }
 
+/**
+ * gst_video_decoder_proxy_getcaps:
+ * @decoder: a #GstVideoDecoder
+ * @caps: (allow-none): initial caps
+ * @filter: (allow-none): filter caps
+ *
+ * Returns caps that express @caps (or sink template caps if @caps == NULL)
+ * restricted to resolution/format/... combinations supported by downstream
+ * elements.
+ *
+ * Returns: (transfer-full): a #GstCaps owned by caller
+ *
+ * @Since: 1.6
+ */
+GstCaps *
+gst_video_decoder_proxy_getcaps (GstVideoDecoder * decoder, GstCaps * caps,
+    GstCaps * filter)
+{
+  return __gst_video_element_proxy_getcaps (GST_ELEMENT_CAST (decoder),
+      GST_VIDEO_DECODER_SINK_PAD (decoder),
+      GST_VIDEO_DECODER_SRC_PAD (decoder), caps, filter);
+}
+
+static GstCaps *
+gst_video_decoder_sink_getcaps (GstVideoDecoder * decoder, GstCaps * filter)
+{
+  GstVideoDecoderClass *klass;
+  GstCaps *caps;
+
+  klass = GST_VIDEO_DECODER_GET_CLASS (decoder);
+
+  if (klass->getcaps)
+    caps = klass->getcaps (decoder, filter);
+  else
+    caps = gst_video_decoder_proxy_getcaps (decoder, NULL, filter);
+
+  GST_LOG_OBJECT (decoder, "Returning caps %" GST_PTR_FORMAT, caps);
+
+  return caps;
+}
+
 static gboolean
 gst_video_decoder_sink_query_default (GstVideoDecoder * decoder,
     GstQuery * query)
@@ -1615,15 +1656,12 @@ gst_video_decoder_sink_query_default (GstVideoDecoder * decoder,
       break;
     }
     case GST_QUERY_CAPS:{
-      GstCaps *filter;
-      GstCaps *result;
+      GstCaps *filter, *caps;
 
       gst_query_parse_caps (query, &filter);
-      result = __gst_video_element_proxy_getcaps (GST_ELEMENT_CAST (decoder),
-          GST_VIDEO_DECODER_SINK_PAD (decoder),
-          GST_VIDEO_DECODER_SRC_PAD (decoder), NULL, filter);
-      gst_query_set_caps_result (query, result);
-      gst_caps_unref (result);
+      caps = gst_video_decoder_sink_getcaps (decoder, filter);
+      gst_query_set_caps_result (query, caps);
+      gst_caps_unref (caps);
       res = TRUE;
       break;
     }

gst-libs/gst/video/gstvideodecoder.h

@@ -256,6 +256,11 @@ struct _GstVideoDecoder
  *                  return TRUE if the query could be performed. Subclasses
  *                  should chain up to the parent implementation to invoke the
  *                  default handler. Since 1.4
+ * @getcaps:        Optional.
+ *                  Allows for a custom sink getcaps implementation.
+ *                  If not implemented, default returns
+ *                  gst_video_decoder_proxy_getcaps
+ *                  applied to sink template caps.
  *
  * Subclasses can override any of the available virtual methods or not, as
  * needed. At minimum @handle_frame needs to be overridden, and @set_format
@@ -312,9 +317,12 @@ struct _GstVideoDecoderClass
   gboolean      (*src_query)      (GstVideoDecoder *decoder,
 				   GstQuery *query);
 
+  GstCaps*      (*getcaps)        (GstVideoDecoder *decoder,
+                                   GstCaps *filter);
+
 
   /*< private >*/
-  void         *padding[GST_PADDING_LARGE-3];
+  void         *padding[GST_PADDING_LARGE-4];
 };
 
 GType    gst_video_decoder_get_type (void);
@@ -398,6 +406,11 @@ void             gst_video_decoder_merge_tags (GstVideoDecoder *decoder,
                                                const GstTagList *tags,
                                                GstTagMergeMode mode);
 
+GstCaps *        gst_video_decoder_proxy_getcaps (GstVideoDecoder * decoder,
+						  GstCaps         * caps,
+                                                  GstCaps         * filter);
+
+
 G_END_DECLS
 
 #endif

tests/check/libs/videodecoder.c

@@ -989,6 +989,42 @@ GST_START_TEST (videodecoder_query_caps_with_range_caps_peer)
 
 GST_END_TEST;
 
+#define GETCAPS_CAPS_STR "video/x-test-custom, somefield=(string)getcaps"
+static GstCaps *
+_custom_video_decoder_getcaps (GstVideoDecoder * dec, GstCaps * filter)
+{
+  return gst_caps_from_string (GETCAPS_CAPS_STR);
+}
+
+GST_START_TEST (videodecoder_query_caps_with_custom_getcaps)
+{
+  GstCaps *caps;
+  GstVideoDecoderClass *klass;
+  GstCaps *expected_caps;
+
+  setup_videodecodertester (&sinktemplate_restricted, NULL);
+
+  klass = GST_VIDEO_DECODER_CLASS (GST_VIDEO_DECODER_GET_CLASS (dec));
+  klass->getcaps = _custom_video_decoder_getcaps;
+
+  gst_pad_set_active (mysrcpad, TRUE);
+  gst_element_set_state (dec, GST_STATE_PLAYING);
+  gst_pad_set_active (mysinkpad, TRUE);
+
+  caps = gst_pad_peer_query_caps (mysrcpad, NULL);
+  fail_unless (caps != NULL);
+
+  expected_caps = gst_caps_from_string (GETCAPS_CAPS_STR);
+  fail_unless (gst_caps_is_equal (expected_caps, caps));
+  gst_caps_unref (expected_caps);
+  gst_caps_unref (caps);
+
+  cleanup_videodecodertest ();
+}
+
+GST_END_TEST;
+
+
 static Suite *
 gst_videodecoder_suite (void)
 {
@@ -999,6 +1035,7 @@ gst_videodecoder_suite (void)
 
   tcase_add_test (tc, videodecoder_query_caps_with_fixed_caps_peer);
   tcase_add_test (tc, videodecoder_query_caps_with_range_caps_peer);
+  tcase_add_test (tc, videodecoder_query_caps_with_custom_getcaps);
 
   tcase_add_test (tc, videodecoder_playback);
   tcase_add_test (tc, videodecoder_playback_with_events);

win32/common/libgstvideo.def

@@ -114,6 +114,7 @@ EXPORTS
 	gst_video_decoder_have_frame
 	gst_video_decoder_merge_tags
 	gst_video_decoder_negotiate
+	gst_video_decoder_proxy_getcaps
 	gst_video_decoder_release_frame
 	gst_video_decoder_set_estimate_rate
 	gst_video_decoder_set_latency