videoaggregator: Expose vmethods to set converters and prepare/clean frames

This gives more flexibility to the subclasses and permits to remove the
GstVideoAggregatorClass->disable_frame_conversion ugly API.

WARNING: This breaks the API as it removes the disable_frame_conversion
field

API:
  + GstVideoAggregatorClass->find_best_format
  + GstVideoAggregatorPadClass->set_format
  + GstVideoAggregatorPadClass->prepare_frame
  + GstVideoAggregatorPadClass->clean_frame

  - GstVideoAggregatorClass->disable_frame_conversion

https://bugzilla.gnome.org/show_bug.cgi?id=740768

ext/gl/gstglmixer.c

@@ -87,11 +87,17 @@ static void
 gst_gl_mixer_pad_class_init (GstGLMixerPadClass * klass)
 {
   GObjectClass *gobject_class = (GObjectClass *) klass;
+  GstVideoAggregatorPadClass *vaggpad_class =
+      (GstVideoAggregatorPadClass *) klass;
 
   gobject_class->set_property = gst_gl_mixer_pad_set_property;
   gobject_class->get_property = gst_gl_mixer_pad_get_property;
 
   gobject_class->finalize = gst_gl_mixer_pad_finalize;
+
+  vaggpad_class->set_info = NULL;
+  vaggpad_class->prepare_frame = NULL;
+  vaggpad_class->clean_frame = NULL;
 }
 
 static void
@@ -592,10 +598,10 @@ gst_gl_mixer_class_init (GstGLMixerClass * klass)
   agg_class->stop = gst_gl_mixer_stop;
   agg_class->start = gst_gl_mixer_start;
 
-  videoaggregator_class->disable_frame_conversion = TRUE;
   videoaggregator_class->aggregate_frames = gst_gl_mixer_aggregate_frames;
   videoaggregator_class->get_output_buffer = gst_gl_mixer_get_output_buffer;
   videoaggregator_class->negotiated_caps = _negotiated_caps;
+  videoaggregator_class->find_best_format = NULL;
 
   g_object_class_install_property (gobject_class, PROP_CONTEXT,
       g_param_spec_object ("context",

gst-libs/gst/video/gstvideoaggregator.c

@@ -131,6 +131,63 @@ _flush_pad (GstAggregatorPad * aggpad, GstAggregator * aggregator)
   return TRUE;
 }
 
+static gboolean
+gst_video_aggregator_pad_set_info (GstVideoAggregatorPad * pad,
+    GstVideoAggregator * vagg G_GNUC_UNUSED,
+    GstVideoInfo * current_info, GstVideoInfo * wanted_info)
+{
+  gchar *colorimetry, *best_colorimetry;
+  const gchar *chroma, *best_chroma;
+
+  if (!current_info->finfo)
+    return TRUE;
+
+  if (GST_VIDEO_INFO_FORMAT (current_info) == GST_VIDEO_FORMAT_UNKNOWN)
+    return TRUE;
+
+  if (pad->priv->convert)
+    gst_video_converter_free (pad->priv->convert);
+
+  pad->priv->convert = NULL;
+
+  colorimetry = gst_video_colorimetry_to_string (&(current_info->colorimetry));
+  chroma = gst_video_chroma_to_string (current_info->chroma_site);
+
+  best_colorimetry =
+      gst_video_colorimetry_to_string (&(wanted_info->colorimetry));
+  best_chroma = gst_video_chroma_to_string (wanted_info->chroma_site);
+
+  if (GST_VIDEO_INFO_FORMAT (wanted_info) !=
+      GST_VIDEO_INFO_FORMAT (current_info)
+      || g_strcmp0 (colorimetry, best_colorimetry)
+      || g_strcmp0 (chroma, best_chroma)) {
+    GstVideoInfo tmp_info = *current_info;
+
+    tmp_info.finfo = wanted_info->finfo;
+    tmp_info.chroma_site = wanted_info->chroma_site;
+    tmp_info.colorimetry = wanted_info->colorimetry;
+
+    GST_DEBUG_OBJECT (pad, "This pad will be converted from %d to %d",
+        GST_VIDEO_INFO_FORMAT (current_info),
+        GST_VIDEO_INFO_FORMAT (wanted_info));
+    pad->priv->convert =
+        gst_video_converter_new (current_info, &tmp_info, NULL);
+    pad->need_conversion_update = TRUE;
+    if (!pad->priv->convert) {
+      g_free (colorimetry);
+      g_free (best_colorimetry);
+      GST_WARNING ("No path found for conversion");
+      return FALSE;
+    }
+  } else {
+    GST_DEBUG_OBJECT (pad, "This pad will not need conversion");
+  }
+  g_free (colorimetry);
+  g_free (best_colorimetry);
+
+  return TRUE;
+}
+
 static void
 gst_videoaggregator_pad_finalize (GObject * o)
 {
@@ -143,6 +200,79 @@ gst_videoaggregator_pad_finalize (GObject * o)
   G_OBJECT_CLASS (gst_videoaggregator_pad_parent_class)->finalize (o);
 }
 
+static gboolean
+gst_video_aggregator_pad_prepare_frame (GstVideoAggregatorPad * pad,
+    GstVideoAggregator * vagg)
+{
+  guint outsize;
+  GstVideoFrame *converted_frame;
+  GstBuffer *converted_buf = NULL;
+  GstVideoFrame *frame = g_slice_new0 (GstVideoFrame);
+  static GstAllocationParams params = { 0, 15, 0, 0, };
+
+  if (!gst_video_frame_map (frame, &pad->buffer_vinfo, pad->buffer,
+          GST_MAP_READ)) {
+    GST_WARNING_OBJECT (vagg, "Could not map input buffer");
+  }
+
+  if (pad->priv->convert) {
+    gint converted_size;
+
+    converted_frame = g_slice_new0 (GstVideoFrame);
+
+    /* We wait until here to set the conversion infos, in case vagg->info changed */
+    if (pad->need_conversion_update) {
+      pad->conversion_info = vagg->info;
+      gst_video_info_set_format (&(pad->conversion_info),
+          GST_VIDEO_INFO_FORMAT (&vagg->info), pad->info.width,
+          pad->info.height);
+      pad->need_conversion_update = FALSE;
+    }
+
+    converted_size = pad->conversion_info.size;
+    outsize = GST_VIDEO_INFO_SIZE (&vagg->info);
+    converted_size = converted_size > outsize ? converted_size : outsize;
+    converted_buf = gst_buffer_new_allocate (NULL, converted_size, &params);
+
+    if (!gst_video_frame_map (converted_frame, &(pad->conversion_info),
+            converted_buf, GST_MAP_READWRITE)) {
+      GST_WARNING_OBJECT (vagg, "Could not map converted frame");
+
+      g_slice_free (GstVideoFrame, converted_frame);
+      gst_video_frame_unmap (frame);
+      g_slice_free (GstVideoFrame, frame);
+      return FALSE;
+    }
+
+    gst_video_converter_frame (pad->priv->convert, frame, converted_frame);
+    pad->converted_buffer = converted_buf;
+    gst_video_frame_unmap (frame);
+    g_slice_free (GstVideoFrame, frame);
+  } else {
+    converted_frame = frame;
+  }
+
+  pad->aggregated_frame = converted_frame;
+
+  return TRUE;
+}
+
+static void
+gst_video_aggregator_pad_clean_frame (GstVideoAggregatorPad * pad,
+    GstVideoAggregator * vagg)
+{
+  if (pad->aggregated_frame) {
+    gst_video_frame_unmap (pad->aggregated_frame);
+    g_slice_free (GstVideoFrame, pad->aggregated_frame);
+    pad->aggregated_frame = NULL;
+  }
+
+  if (pad->converted_buffer) {
+    gst_buffer_unref (pad->converted_buffer);
+    pad->converted_buffer = NULL;
+  }
+}
+
 static void
 gst_videoaggregator_pad_class_init (GstVideoAggregatorPadClass * klass)
 {
@@ -161,6 +291,10 @@ gst_videoaggregator_pad_class_init (GstVideoAggregatorPadClass * klass)
   g_type_class_add_private (klass, sizeof (GstVideoAggregatorPadPrivate));
 
   aggpadclass->flush = GST_DEBUG_FUNCPTR (_flush_pad);
+  klass->set_info = GST_DEBUG_FUNCPTR (gst_video_aggregator_pad_set_info);
+  klass->prepare_frame =
+      GST_DEBUG_FUNCPTR (gst_video_aggregator_pad_prepare_frame);
+  klass->clean_frame = GST_DEBUG_FUNCPTR (gst_video_aggregator_pad_clean_frame);
 }
 
 static void
@@ -268,8 +402,8 @@ G_DEFINE_ABSTRACT_TYPE_WITH_CODE (GstVideoAggregator, gst_videoaggregator,
         gst_videoaggregator_child_proxy_init));
 
 static void
-_find_best_video_format (GstVideoAggregator * vagg, GstCaps * downstream_caps,
+gst_videoaggreagator_find_best_format (GstVideoAggregator * vagg,
-    GstVideoInfo * best_info, GstVideoFormat * best_format,
+    GstCaps * downstream_caps, GstVideoInfo * best_info,
     gboolean * at_least_one_alpha)
 {
   GList *tmp;
@@ -326,11 +460,9 @@ _find_best_video_format (GstVideoAggregator * vagg, GstCaps * downstream_caps,
     /* If that pad is the first with alpha, set it as the new best format */
     if (!need_alpha && (pad->info.finfo->flags & GST_VIDEO_FORMAT_FLAG_ALPHA)) {
       need_alpha = TRUE;
-      *best_format = GST_VIDEO_INFO_FORMAT (&pad->info);
       *best_info = pad->info;
       best_format_number = format_number;
     } else if (format_number > best_format_number) {
-      *best_format = GST_VIDEO_INFO_FORMAT (&pad->info);
       *best_info = pad->info;
       best_format_number = format_number;
     }
@@ -349,17 +481,16 @@ static gboolean
 gst_videoaggregator_update_converters (GstVideoAggregator * vagg)
 {
   GList *tmp;
-  GstVideoAggregatorPad *pad;
   GstVideoFormat best_format;
   GstVideoInfo best_info;
   gboolean at_least_one_alpha = FALSE;
   GstCaps *downstream_caps;
-  gchar *best_colorimetry;
-  const gchar *best_chroma;
-  GstElementClass *klass = GST_ELEMENT_GET_CLASS (vagg);
-  GstVideoAggregatorClass *vagg_klass = (GstVideoAggregatorClass *) klass;
   GstAggregator *agg = GST_AGGREGATOR (vagg);
 
+  GstVideoAggregatorClass *vagg_class = GST_VIDEO_AGGREGATOR_GET_CLASS (vagg);
+  GstVideoAggregatorPadClass *vaggpad_class = g_type_class_peek
+      (GST_AGGREGATOR_GET_CLASS (vagg)->sinkpads_type);
+
   best_format = GST_VIDEO_FORMAT_UNKNOWN;
   gst_video_info_init (&best_info);
 
@@ -374,10 +505,13 @@ gst_videoaggregator_update_converters (GstVideoAggregator * vagg)
   }
 
 
-  if (vagg_klass->disable_frame_conversion == FALSE)
+  if (vagg_class->find_best_format) {
-    _find_best_video_format (vagg, downstream_caps, &best_info, &best_format,
+    vagg_class->find_best_format (vagg, downstream_caps, &best_info,
         &at_least_one_alpha);
 
+    best_format = GST_VIDEO_INFO_FORMAT (&best_info);
+  }
+
   if (best_format == GST_VIDEO_FORMAT_UNKNOWN) {
     downstream_caps = gst_caps_fixate (downstream_caps);
     gst_video_info_from_caps (&best_info, downstream_caps);
@@ -396,68 +530,25 @@ gst_videoaggregator_update_converters (GstVideoAggregator * vagg)
 
   vagg->info = best_info;
 
-  /* short circuit */
-  if (vagg_klass->disable_frame_conversion)
-    return TRUE;
-
-  best_colorimetry = gst_video_colorimetry_to_string (&(best_info.colorimetry));
-  best_chroma = gst_video_chroma_to_string (best_info.chroma_site);
-
   GST_DEBUG_OBJECT (vagg,
-      "The output format will now be : %d with colorimetry : %s and chroma : %s",
+      "The output format will now be : %d with chroma : %s",
-      best_format, best_colorimetry, best_chroma);
+      best_format, gst_video_chroma_to_string (best_info.chroma_site));
 
-  /* Then browse the sinks once more, setting or unsetting conversion if needed */
+  if (vaggpad_class->set_info) {
-  GST_OBJECT_LOCK (vagg);
+    GST_OBJECT_LOCK (vagg);
-  for (tmp = GST_ELEMENT (vagg)->sinkpads; tmp; tmp = tmp->next) {
+    /* Then browse the sinks once more, setting or unsetting conversion if needed */
-    gchar *colorimetry;
+    for (tmp = GST_ELEMENT (vagg)->sinkpads; tmp; tmp = tmp->next) {
-    const gchar *chroma;
+      GstVideoAggregatorPad *pad = GST_VIDEO_AGGREGATOR_PAD (tmp->data);
 
-    pad = tmp->data;
+      if (!vaggpad_class->set_info (pad, vagg, &pad->info, &best_info)) {
-
-    if (!pad->info.finfo)
-      continue;
-
-    if (GST_VIDEO_INFO_FORMAT (&pad->info) == GST_VIDEO_FORMAT_UNKNOWN)
-      continue;
-
-    if (pad->priv->convert)
-      gst_video_converter_free (pad->priv->convert);
-
-    pad->priv->convert = NULL;
-
-    colorimetry = gst_video_colorimetry_to_string (&(pad->info.colorimetry));
-    chroma = gst_video_chroma_to_string (pad->info.chroma_site);
-
-    if (best_format != GST_VIDEO_INFO_FORMAT (&pad->info) ||
-        g_strcmp0 (colorimetry, best_colorimetry) ||
-        g_strcmp0 (chroma, best_chroma)) {
-      GstVideoInfo tmp_info = pad->info;
-      tmp_info.finfo = best_info.finfo;
-      tmp_info.chroma_site = best_info.chroma_site;
-      tmp_info.colorimetry = best_info.colorimetry;
-
-      GST_DEBUG_OBJECT (pad, "This pad will be converted from %d to %d",
-          GST_VIDEO_INFO_FORMAT (&pad->info),
-          GST_VIDEO_INFO_FORMAT (&best_info));
-      pad->priv->convert =
-          gst_video_converter_new (&pad->info, &tmp_info, NULL);
-      pad->need_conversion_update = TRUE;
-      if (!pad->priv->convert) {
-        g_free (colorimetry);
-        g_free (best_colorimetry);
-        GST_WARNING ("No path found for conversion");
         GST_OBJECT_UNLOCK (vagg);
+
         return FALSE;
       }
-    } else {
-      GST_DEBUG_OBJECT (pad, "This pad will not need conversion");
     }
-    g_free (colorimetry);
+    GST_OBJECT_UNLOCK (vagg);
   }
-  GST_OBJECT_UNLOCK (vagg);
 
-  g_free (best_colorimetry);
   return TRUE;
 }
 
@@ -990,7 +1081,8 @@ static gboolean
 prepare_frames (GstVideoAggregator * vagg, GstVideoAggregatorPad * pad)
 {
   GstAggregatorPad *bpad = GST_AGGREGATOR_PAD (pad);
-  GstVideoAggregatorClass *vagg_klass = GST_VIDEO_AGGREGATOR_GET_CLASS (vagg);
+  GstVideoAggregatorPadClass *vaggpad_class =
+      GST_VIDEO_AGGREGATOR_PAD_GET_CLASS (pad);
 
   if (pad->buffer != NULL) {
     GstClockTime timestamp;
@@ -1007,56 +1099,8 @@ prepare_frames (GstVideoAggregator * vagg, GstVideoAggregatorPad * pad)
     if (GST_CLOCK_TIME_IS_VALID (stream_time))
       gst_object_sync_values (GST_OBJECT (pad), stream_time);
 
-    if (!vagg_klass->disable_frame_conversion) {
+    if (vaggpad_class->prepare_frame) {
-      guint outsize;
+      return vaggpad_class->prepare_frame (pad, vagg);
-      GstVideoFrame *converted_frame;
-      GstBuffer *converted_buf = NULL;
-      GstVideoFrame *frame = g_slice_new0 (GstVideoFrame);
-      static GstAllocationParams params = { 0, 15, 0, 0, };
-
-      if (!gst_video_frame_map (frame, &pad->buffer_vinfo, pad->buffer,
-              GST_MAP_READ)) {
-        GST_WARNING_OBJECT (vagg, "Could not map input buffer");
-      }
-
-      if (pad->priv->convert) {
-        gint converted_size;
-
-        converted_frame = g_slice_new0 (GstVideoFrame);
-
-        /* We wait until here to set the conversion infos, in case vagg->info changed */
-        if (pad->need_conversion_update) {
-          pad->conversion_info = vagg->info;
-          gst_video_info_set_format (&(pad->conversion_info),
-              GST_VIDEO_INFO_FORMAT (&vagg->info), pad->info.width,
-              pad->info.height);
-          pad->need_conversion_update = FALSE;
-        }
-
-        converted_size = pad->conversion_info.size;
-        outsize = GST_VIDEO_INFO_SIZE (&vagg->info);
-        converted_size = converted_size > outsize ? converted_size : outsize;
-        converted_buf = gst_buffer_new_allocate (NULL, converted_size, &params);
-
-        if (!gst_video_frame_map (converted_frame, &(pad->conversion_info),
-                converted_buf, GST_MAP_READWRITE)) {
-          GST_WARNING_OBJECT (vagg, "Could not map converted frame");
-
-          g_slice_free (GstVideoFrame, converted_frame);
-          gst_video_frame_unmap (frame);
-          g_slice_free (GstVideoFrame, frame);
-          return FALSE;
-        }
-
-        gst_video_converter_frame (pad->priv->convert, frame, converted_frame);
-        pad->converted_buffer = converted_buf;
-        gst_video_frame_unmap (frame);
-        g_slice_free (GstVideoFrame, frame);
-      } else {
-        converted_frame = frame;
-      }
-
-      pad->aggregated_frame = converted_frame;
     }
   }
 
@@ -1066,16 +1110,10 @@ prepare_frames (GstVideoAggregator * vagg, GstVideoAggregatorPad * pad)
 static gboolean
 clean_pad (GstVideoAggregator * vagg, GstVideoAggregatorPad * pad)
 {
-  if (pad->aggregated_frame) {
+  GstVideoAggregatorPadClass *vaggpad_class =
-    gst_video_frame_unmap (pad->aggregated_frame);
+      GST_VIDEO_AGGREGATOR_PAD_GET_CLASS (pad);
-    g_slice_free (GstVideoFrame, pad->aggregated_frame);
-    pad->aggregated_frame = NULL;
-  }
 
-  if (pad->converted_buffer) {
+  vaggpad_class->clean_frame (pad, vagg);
-    gst_buffer_unref (pad->converted_buffer);
-    pad->converted_buffer = NULL;
-  }
 
   return TRUE;
 }
@@ -1088,6 +1126,8 @@ gst_videoaggregator_do_aggregate (GstVideoAggregator * vagg,
   GstFlowReturn ret = GST_FLOW_OK;
   GstElementClass *klass = GST_ELEMENT_GET_CLASS (vagg);
   GstVideoAggregatorClass *vagg_klass = (GstVideoAggregatorClass *) klass;
+  GstVideoAggregatorPadClass *vaggpad_class = g_type_class_peek
+      (GST_AGGREGATOR_CLASS (klass)->sinkpads_type);
 
   g_assert (vagg_klass->aggregate_frames != NULL);
   g_assert (vagg_klass->get_output_buffer != NULL);
@@ -1108,8 +1148,10 @@ gst_videoaggregator_do_aggregate (GstVideoAggregator * vagg,
 
   ret = vagg_klass->aggregate_frames (vagg, *outbuf);
 
-  gst_aggregator_iterate_sinkpads (GST_AGGREGATOR (vagg),
+  if (vaggpad_class->clean_frame) {
-      (GstAggregatorPadForeachFunc) clean_pad, NULL);
+    gst_aggregator_iterate_sinkpads (GST_AGGREGATOR (vagg),
+        (GstAggregatorPadForeachFunc) clean_pad, NULL);
+  }
 
   return ret;
 }
@@ -1838,6 +1880,7 @@ gst_videoaggregator_class_init (GstVideoAggregatorClass * klass)
   agg_class->src_event = gst_videoaggregator_src_event;
   agg_class->src_query = gst_videoaggregator_src_query;
 
+  klass->find_best_format = gst_videoaggreagator_find_best_format;
   klass->get_output_buffer = gst_videoaggregator_get_output_buffer;
 
   /* Register the pad class */

gst-libs/gst/video/gstvideoaggregator.h

@@ -30,8 +30,6 @@
 #include <gst/video/video.h>
 #include <gst/base/gstaggregator.h>
 
-#include "gstvideoaggregatorpad.h"
-
 G_BEGIN_DECLS
 
 #define GST_TYPE_VIDEO_AGGREGATOR (gst_videoaggregator_get_type())
@@ -50,6 +48,8 @@ typedef struct _GstVideoAggregator GstVideoAggregator;
 typedef struct _GstVideoAggregatorClass GstVideoAggregatorClass;
 typedef struct _GstVideoAggregatorPrivate GstVideoAggregatorPrivate;
 
+#include "gstvideoaggregatorpad.h"
+
 /**
  * GstVideoAggregator:
  * @info: The #GstVideoInfo representing the currently set
@@ -70,9 +70,6 @@ struct _GstVideoAggregator
 
 /**
  * GstVideoAggregatorClass:
- * @disable_frame_conversion: Optional.
- *                            Allows subclasses to disable the frame colorspace
- *                            conversion feature
  * @update_caps:              Optional.
  *                            Lets subclasses update the #GstCaps representing
  *                            the src pad caps before usage.  Return %NULL to indicate failure.
@@ -87,6 +84,8 @@ struct _GstVideoAggregator
  *                            the #aggregate_frames vmethod.
  * @negotiated_caps:          Optional.
  *                            Notifies subclasses what caps format has been negotiated
+ * @find_best_format:         Optional.
+ *                            Lets subclasses decide of the best common format to use.
  **/
 struct _GstVideoAggregatorClass
 {
@@ -94,8 +93,6 @@ struct _GstVideoAggregatorClass
   GstAggregatorClass parent_class;
 
   /*< public >*/
-  gboolean           disable_frame_conversion;
-
   GstCaps *          (*update_caps)               (GstVideoAggregator *  videoaggregator,
                                                    GstCaps            *  caps);
   GstFlowReturn      (*aggregate_frames)          (GstVideoAggregator *  videoaggregator,
@@ -104,6 +101,10 @@ struct _GstVideoAggregatorClass
                                                    GstBuffer          ** outbuffer);
   gboolean           (*negotiated_caps)           (GstVideoAggregator *  videoaggregator,
                                                    GstCaps            *  caps);
+  void               (*find_best_format)          (GstVideoAggregator *  vagg,
+                                                   GstCaps            *  downstream_caps,
+                                                   GstVideoInfo       *  best_info,
+                                                   gboolean           *  at_least_one_alpha);
   /* < private > */
   gpointer            _gst_reserved[GST_PADDING];
 };

gst-libs/gst/video/gstvideoaggregatorpad.h

@@ -17,7 +17,7 @@
  * Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
- 
+
 #ifndef __GST_VIDEO_AGGREGATOR_PAD_H__
 #define __GST_VIDEO_AGGREGATOR_PAD_H__
 
@@ -25,6 +25,7 @@
 #include <gst/video/video.h>
 
 #include <gst/base/gstaggregator.h>
+#include "gstvideoaggregator.h"
 
 G_BEGIN_DECLS
 
@@ -37,6 +38,8 @@ G_BEGIN_DECLS
         (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_VIDEO_AGGREGATOR_PAD))
 #define GST_IS_VIDEO_AGGREGATOR_PAD_CLASS(klass) \
         (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_VIDEO_AGGREGATOR_PAD))
+#define GST_VIDEO_AGGREGATOR_PAD_GET_CLASS(obj) \
+        (G_TYPE_INSTANCE_GET_CLASS((obj),GST_TYPE_VIDEO_AGGREGATOR_PAD,GstVideoAggregatorPadClass))
 
 typedef struct _GstVideoAggregatorPad GstVideoAggregatorPad;
 typedef struct _GstVideoAggregatorPadClass GstVideoAggregatorPadClass;
@@ -77,9 +80,28 @@ struct _GstVideoAggregatorPad
   gpointer          _gst_reserved[GST_PADDING];
 };
 
+/**
+ * GstVideoAggregatorPadClass:
+ *
+ * @set_info: Lets subclass set a converter on the pad,
+ *                 right after a new format has been negotiated.
+ * @prepare_frame: Prepare the frame from the pad buffer (if any)
+ *                 and sets it to @aggregated_frame
+ * @clean_frame:   clean the frame previously prepared in prepare_frame
+ */
 struct _GstVideoAggregatorPadClass
 {
   GstAggregatorPadClass parent_class;
+  gboolean           (*set_info)              (GstVideoAggregatorPad * pad,
+                                               GstVideoAggregator    * videoaggregator,
+                                               GstVideoInfo          * current_info,
+                                               GstVideoInfo          * wanted_info);
+
+  gboolean           (*prepare_frame)         (GstVideoAggregatorPad * pad,
+                                               GstVideoAggregator    * videoaggregator);
+
+  void               (*clean_frame)           (GstVideoAggregatorPad * pad,
+                                               GstVideoAggregator    * videoaggregator);
 
   gpointer          _gst_reserved[GST_PADDING];
 };