gstvaapivideomemory: allocator's image size getter

Add the method gst_allocator_get_vaapi_image_size() for the
GstVaapiVideoAllocator, which gets the size of the allocated images with the
current video info.

This method replaces the direct call to the allocator's image info when the
pool is configured.

gst/vaapi/gstvaapipluginbase.c

@@ -832,10 +832,8 @@ gst_vaapi_plugin_base_decide_allocation (GstVaapiPluginBase * plugin,
   if (!pool) {
     if (!ensure_srcpad_allocator (plugin, &vi))
       goto error_create_allocator;
-
     /* Update video size with allocator's image size */
-    size = GST_VIDEO_INFO_SIZE (&GST_VAAPI_VIDEO_ALLOCATOR_CAST
-        (plugin->srcpad_allocator)->image_info);
+    gst_allocator_get_vaapi_image_size (plugin->srcpad_allocator, &size);
     pool = gst_vaapi_plugin_base_create_pool (plugin, caps, size, min, max,
         pool_options, plugin->srcpad_allocator);
     if (!pool)

gst/vaapi/gstvaapivideomemory.c

@@ -1036,6 +1036,32 @@ gst_allocator_set_vaapi_video_info (GstAllocator * allocator,
   return TRUE;
 }
 
+/**
+ * gst_allocator_get_vaapi_image_size:
+ * @allocator: a #GstAllocator instance.
+ * @size: (out) (optional): the VA image size created by @allocator.
+ *
+ * This function gets the size of the VA images instantiated by the
+ * @allocator.
+ *
+ * Returns: %TRUE if @allocator is VA valid
+ **/
+gboolean
+gst_allocator_get_vaapi_image_size (GstAllocator * allocator, guint * size)
+{
+  GstVaapiVideoAllocator *alloc;
+
+  g_return_val_if_fail (GST_IS_ALLOCATOR (allocator), FALSE);
+
+  if (g_strcmp0 (allocator->mem_type, GST_VAAPI_VIDEO_MEMORY_NAME))
+    return FALSE;
+  alloc = GST_VAAPI_VIDEO_ALLOCATOR_CAST (allocator);
+  if (alloc && size)
+    *size = GST_VIDEO_INFO_SIZE (&alloc->image_info);
+
+  return TRUE;
+}
+
 gboolean
 gst_vaapi_is_dmabuf_allocator (GstAllocator * allocator)
 {

gst/vaapi/gstvaapivideomemory.h

@@ -216,6 +216,10 @@ gboolean
 gst_allocator_set_vaapi_video_info (GstAllocator * allocator,
     const GstVideoInfo * vip, guint flags);
 
+G_GNUC_INTERNAL
+gboolean
+gst_allocator_get_vaapi_image_size (GstAllocator * allocator, guint * size);
+
 G_GNUC_INTERNAL
 gboolean
 gst_vaapi_is_dmabuf_allocator (GstAllocator * allocator);