lavfi: add outlink helper functions.

These wrappers cost nothing, they make the namespace more
consistent and they will be useful if/when locking becomes
necessary.

libavfilter/filters.h

@@ -26,6 +26,7 @@
  */
 
 #include "avfilter.h"
+#include "internal.h"
 
 /**
  * Special return code when activate() did not do anything.
@@ -139,4 +140,24 @@ int ff_inlink_acknowledge_status(AVFilterLink *link, int *rstatus, int64_t *rpts
  */
 void ff_inlink_request_frame(AVFilterLink *link);
 
+/**
+ * Test if a frame is wanted on an output link.
+ */
+static inline int ff_outlink_frame_wanted(AVFilterLink *link)
+{
+    return link->frame_wanted_out;
+}
+
+/**
+ * Set the status field of a link from the source filter.
+ * The pts should reflect the timestamp of the status change,
+ * in link time base and relative to the frames timeline.
+ * In particular, for AVERROR_EOF, it should reflect the
+ * end time of the last frame.
+ */
+static inline void ff_outlink_set_status(AVFilterLink *link, int status, int64_t pts)
+{
+    ff_avfilter_link_set_in_status(link, status, pts);
+}
+
 #endif /* AVFILTER_FILTERS_H */