diff --git a/libavcodec/h263.c b/libavcodec/h263.c
index ad54203930..d1ea3946d9 100644
--- a/libavcodec/h263.c
+++ b/libavcodec/h263.c
@@ -5751,6 +5751,8 @@ static int decode_user_data(MpegEncContext *s, GetBitContext *gb){
         s->divx_version= ver;
         s->divx_build= build;
         s->divx_packed= e==3 && last=='p';
+        if(s->divx_packed)
+            av_log(s->avctx, AV_LOG_WARNING, "Invalid and inefficient vfw-avi packed B frames detected\n");
     }
 
     /* ffmpeg detection */