Implement avfilter_graph_check_validity().

Originally committed as revision 16809 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavfilter/avfiltergraph.h

@@ -44,6 +44,16 @@ AVFilterContext *avfilter_graph_get_filter(AVFilterGraph *graph, char *name);
  */
 int avfilter_graph_add_filter(AVFilterGraph *graphctx, AVFilterContext *filter);
 
+/**
+ * Check for the validity of \p graph.
+ *
+ * A graph is considered valid if all its input and output pads are
+ * connected.
+ *
+ * @return 0 in case of success, a negative value otherwise
+ */
+int avfilter_graph_check_validity(AVFilterGraph *graphctx, AVClass *log_ctx);
+
 /**
  * Configure the formats of all the links in the graph.
  */