plugins: fix buffer pool reset_buffer() to reset memory resources.

Fix GstVaapiVideoBufferPool::reset_buffer() to reset the underlying
memory resources, and more particularly the VA surface proxy. Most
importantly, the GstVaapiVideoMeta is retained. Cached surface in
memory are released, thus triggering a new allocation the next time
we need to map the buffer.

gst/vaapi/gstvaapivideobufferpool.c

@@ -234,10 +234,10 @@ error_create_memory:
 static void
 gst_vaapi_video_buffer_pool_reset_buffer(GstBufferPool *pool, GstBuffer *buffer)
 {
-    GstVaapiVideoMeta * const meta = gst_buffer_get_vaapi_video_meta(buffer);
+    GstMemory * const mem = gst_buffer_peek_memory(buffer, 0);
 
     /* Release the underlying surface proxy */
-    gst_vaapi_video_meta_set_surface_proxy(meta, NULL);
+    gst_vaapi_video_memory_reset_surface(GST_VAAPI_VIDEO_MEMORY_CAST(mem));
 
     GST_BUFFER_POOL_CLASS(gst_vaapi_video_buffer_pool_parent_class)->
         reset_buffer(pool, buffer);

gst/vaapi/gstvaapivideomemory.c

@@ -258,6 +258,16 @@ gst_vaapi_video_memory_free(GstVaapiVideoMemory *mem)
     g_slice_free(GstVaapiVideoMemory, mem);
 }
 
+void
+gst_vaapi_video_memory_reset_surface(GstVaapiVideoMemory *mem)
+{
+    mem->surface = NULL;
+    gst_vaapi_surface_proxy_replace(&mem->proxy, NULL);
+    if (mem->use_direct_rendering)
+        gst_vaapi_object_replace(&mem->image, NULL);
+    gst_vaapi_video_meta_set_surface_proxy(mem->meta, NULL);
+}
+
 static gpointer
 gst_vaapi_video_memory_map(GstVaapiVideoMemory *mem, gsize maxsize, guint flags)
 {

gst/vaapi/gstvaapivideomemory.h

@@ -96,6 +96,10 @@ gboolean
 gst_video_meta_unmap_vaapi_memory(GstVideoMeta *meta, guint plane,
     GstMapInfo *info);
 
+G_GNUC_INTERNAL
+void
+gst_vaapi_video_memory_reset_surface(GstVaapiVideoMemory *mem);
+
 /* ------------------------------------------------------------------------ */
 /* --- GstVaapiVideoAllocator                                           --- */
 /* ------------------------------------------------------------------------ */