diff --git a/ffmpeg.c b/ffmpeg.c
index 87c3f7a5d3..9575813bca 100644
--- a/ffmpeg.c
+++ b/ffmpeg.c
@@ -1746,6 +1746,7 @@ duplicate_frame:
         pkt.flags |= AV_PKT_FLAG_KEY;
 
         write_frame(s, &pkt, ost);
+        video_size += pkt.size;
     } else {
         int got_packet;
         AVFrame big_picture;