lavfi: use a new field for automatic buffer copy.

The code currently use cur_buf as the target of the copy,
but cur_buf can be cleared by the filter if it has given
the reference away or stored it elsewhere as soon as start_frame.

The code still relies on the fact that the reference is not
destroyed until end_frame. All filters currently follow that condition.
An av_assert1() is added to check it; it should at least cause
very visible errors in valgrind.

1 files changed, 9 insertions, 0 deletions

diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
index 68373fdd6e..0e7111d53b 100644
--- a/libavfilter/avfilter.h
+++ b/libavfilter/avfilter.h
@@ -669,6 +669,15 @@ struct AVFilterLink {
      * called with more samples, it will split them.
      */
     int max_samples;
+
+    /**
+     * The buffer reference currently being received across the link by the
+     * destination filter. This is used internally by the filter system to
+     * allow automatic copying of buffers which do not have sufficient
+     * permissions for the destination. This should not be accessed directly
+     * by the filters.
+     */
+    AVFilterBufferRef *cur_buf_copy;
 };
 
 /**