msdkenc: handle bitrate changes in playing state

When the bitrate is changed in playing state the encoder issues a reconfig
that drains and recreates the underlaying hw encoder instance.
With this set of changes we ensure that all this work is only made when
the bitrate did actually change. It also tries to reuse the vpp buffer
pool and fixes the pool leak spotted when testing this feature.

sys/msdk/gstmsdkenc.c

@@ -1136,6 +1136,28 @@ gst_msdkenc_set_format (GstVideoEncoder * encoder, GstVideoCodecState * state)
         info->height);
     caps = gst_video_info_to_caps (&nv12_info);
 
+    /* If there's an existing pool try to reuse it when is compatible */
+    if (thiz->msdk_converted_pool) {
+      GstStructure *config;
+      GstCaps *pool_caps;
+      gboolean is_pool_compatible = FALSE;
+
+      config = gst_buffer_pool_get_config (thiz->msdk_converted_pool);
+      gst_buffer_pool_config_get_params (config, &pool_caps, NULL, NULL, NULL);
+      if (caps && pool_caps)
+        is_pool_compatible = gst_caps_is_equal (caps, pool_caps);
+      gst_structure_free (config);
+
+      /* If caps are the same then we are done */
+      if (is_pool_compatible) {
+        gst_caps_unref (caps);
+        goto done;
+      }
+      /* Release current pool because we are going to create a new one */
+      gst_object_replace ((GstObject **) & thiz->msdk_converted_pool, NULL);
+    }
+
+    /* Otherwise create a new pool */
     pool =
         gst_msdkenc_create_buffer_pool (thiz, caps, thiz->num_surfaces, FALSE);
 
@@ -1143,6 +1165,7 @@ gst_msdkenc_set_format (GstVideoEncoder * encoder, GstVideoCodecState * state)
     gst_caps_unref (caps);
   }
 
+done:
   return TRUE;
 }
 
@@ -1683,9 +1706,16 @@ gst_msdkenc_set_common_property (GObject * object, guint prop_id,
       thiz->rate_control = g_value_get_enum (value);
       break;
     case GST_MSDKENC_PROP_BITRATE:
-      thiz->bitrate = g_value_get_uint (value);
+    {
-      thiz->reconfig = TRUE;
+      guint bitrate = g_value_get_uint (value);
+      /* Ensure that bitrate changed before triggering a reconfig */
+      if (bitrate != thiz->bitrate) {
+        thiz->bitrate = bitrate;
+        thiz->reconfig = TRUE;
+        GST_DEBUG_OBJECT (thiz, "changed bitrate to %u", bitrate);
+      }
       break;
+    }
     case GST_MSDKENC_PROP_MAX_FRAME_SIZE:
       thiz->max_frame_size = g_value_get_uint (value);
       break;