avfilter: Log an error if avfilter fails to configure a link.

libavfilter/avfilter.c

@@ -163,8 +163,12 @@ int avfilter_config_links(AVFilterContext *filter)
                                                     "callbacks on all outputs\n");
                     return AVERROR(EINVAL);
                 }
-            } else if ((ret = config_link(link)) < 0)
+            } else if ((ret = config_link(link)) < 0) {
+                av_log(link->src, AV_LOG_ERROR,
+                       "Failed to configure output pad on %s\n",
+                       link->src->name);
                 return ret;
+            }
 
             if (link->time_base.num == 0 && link->time_base.den == 0)
                 link->time_base = link->src && link->src->input_count ?
@@ -189,8 +193,12 @@ int avfilter_config_links(AVFilterContext *filter)
             }
 
             if ((config_link = link->dstpad->config_props))
-                if ((ret = config_link(link)) < 0)
+                if ((ret = config_link(link)) < 0) {
+                    av_log(link->src, AV_LOG_ERROR,
+                           "Failed to configure input pad on %s\n",
+                           link->dst->name);
                     return ret;
+                }
 
             link->init_state = AVLINK_INIT;
         }