lavfi: add a preinit callback to filters.

It is necessary for filters with child objects, to set the class
and default options values.

1 files changed, 15 insertions, 0 deletions

diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
index 60662c19ac..73a723d583 100644
--- a/libavfilter/avfilter.h
+++ b/libavfilter/avfilter.h
@@ -195,6 +195,21 @@ typedef struct AVFilter {
      */
 
     /**
+     * Filter pre-initialization function
+     *
+     * This callback will be called immediately after the filter context is
+     * allocated, to allow allocating and initing sub-objects.
+     *
+     * If this callback is not NULL, the uninit callback will be called on
+     * allocation failure.
+     *
+     * @return 0 on success,
+     *         AVERROR code on failure (but the code will be
+     *           dropped and treated as ENOMEM by the calling code)
+     */
+    int (*preinit)(AVFilterContext *ctx);
+
+    /**
      * Filter initialization function.
      *
      * This callback will be called only once during the filter lifetime, after