avfilter: factorize requesting an input frame from multi output filters

Signed-off-by: Marton Balint <cus@passwd.hu>

libavfilter/filters.h

@@ -696,6 +696,21 @@ static inline void ff_outlink_set_status(AVFilterLink *link, int status, int64_t
     } \
 } while (0)
 
+/**
+ * Forward the frame_wanted_out flag from any of the output links to an input link.
+ * If the flag is set on any of the outputs, this macro will return immediately.
+ */
+#define FF_FILTER_FORWARD_WANTED_ANY(filter, inlink) do { \
+    for (int i = 0; i < filter->nb_outputs; i++) { \
+        if (ff_outlink_get_status(filter->outputs[i])) \
+            continue; \
+        if (ff_outlink_frame_wanted(filter->outputs[i])) { \
+            ff_inlink_request_frame(inlink); \
+            return 0; \
+        } \
+    } \
+} while (0)
+
 /**
  * Check for flow control between input and output.
  * This is necessary for filters that may produce several output frames for