lavfi: deprecate avfilter_link_free()

It never makes sense for this function to be called by users.

libavfilter/avfilter.c

@@ -192,7 +192,7 @@ int avfilter_link(AVFilterContext *src, unsigned srcpad,
     return 0;
 }
 
-void avfilter_link_free(AVFilterLink **link)
+static void link_free(AVFilterLink **link)
 {
     FilterLinkInternal *li;
 
@@ -207,6 +207,13 @@ void avfilter_link_free(AVFilterLink **link)
     av_freep(link);
 }
 
+#if FF_API_LINK_PUBLIC
+void avfilter_link_free(AVFilterLink **link)
+{
+    link_free(link);
+}
+#endif
+
 static void update_link_current_pts(FilterLinkInternal *li, int64_t pts)
 {
     AVFilterLink *const link = &li->l;
@@ -763,7 +770,7 @@ static void free_link(AVFilterLink *link)
     ff_formats_unref(&link->outcfg.samplerates);
     ff_channel_layouts_unref(&link->incfg.channel_layouts);
     ff_channel_layouts_unref(&link->outcfg.channel_layouts);
-    avfilter_link_free(&link);
+    link_free(&link);
 }
 
 void avfilter_free(AVFilterContext *filter)

libavfilter/avfilter.h

@@ -676,10 +676,13 @@ struct AVFilterLink {
 int avfilter_link(AVFilterContext *src, unsigned srcpad,
                   AVFilterContext *dst, unsigned dstpad);
 
+#if FF_API_LINK_PUBLIC
 /**
- * Free the link in *link, and set its pointer to NULL.
+ * @deprecated this function should never be called by users
  */
+attribute_deprecated
 void avfilter_link_free(AVFilterLink **link);
+#endif
 
 /**
  * Negotiate the media format, dimensions, etc of all inputs to a filter.

libavfilter/version_major.h

@@ -35,4 +35,6 @@
  * the public API and may change, break or disappear at any time.
  */
 
+#define FF_API_LINK_PUBLIC     (LIBAVFILTER_VERSION_MAJOR < 11)
+
 #endif /* AVFILTER_VERSION_MAJOR_H */