lavfi/bbox: timeline support

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/vf_bbox.c

@@ -116,4 +116,5 @@ AVFilter avfilter_vf_bbox = {
     .query_formats = query_formats,
     .inputs        = bbox_inputs,
     .outputs       = bbox_outputs,
+    .flags         = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC,
 };