lavfi: add ff_inoutlink_check_flow()

libavfilter/avfilter.c

@@ -1559,6 +1559,14 @@ int ff_outlink_get_status(AVFilterLink *link)
     return link->status_in;
 }
 
+int ff_inoutlink_check_flow(AVFilterLink *inlink, AVFilterLink *outlink)
+{
+    return ff_outlink_frame_wanted(outlink) ||
+           ff_inlink_check_available_frame(inlink) ||
+           inlink->status_out;
+}
+
+
 const AVClass *avfilter_get_class(void)
 {
     return &avfilter_class;

libavfilter/filters.h

@@ -258,4 +258,12 @@ static inline void ff_outlink_set_status(AVFilterLink *link, int status, int64_t
     } \
 } while (0)
 
+/**
+ * Check for flow control between input and output.
+ * This is necessary for filters that may produce several output frames for
+ * a single input event, otherwise they may produce them all at once,
+ * causing excessive memory consumption.
+ */
+int ff_inoutlink_check_flow(AVFilterLink *inlink, AVFilterLink *outlink);
+
 #endif /* AVFILTER_FILTERS_H */