-void ff_null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
-void ff_null_draw_slice(AVFilterLink *link, int y, int h, int slice_dir);
-void ff_null_end_frame(AVFilterLink *link);
+int ff_inplace_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
+int ff_null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref);
+int ff_null_draw_slice(AVFilterLink *link, int y, int h, int slice_dir);
+int ff_null_end_frame(AVFilterLink *link);