diff --git a/libavformat/isom.h b/libavformat/isom.h
index 074837f028..e3160d00f8 100644
--- a/libavformat/isom.h
+++ b/libavformat/isom.h
@@ -246,6 +246,7 @@ void ff_mp4_parse_es_descr(AVIOContext *pb, int *es_id);
      (tag) == MKTAG('a', 'i', '1', '3') ||  \
      (tag) == MKTAG('a', 'i', '1', '5') ||  \
      (tag) == MKTAG('a', 'i', '1', '6') ||  \
+     (tag) == MKTAG('a', 'i', 'v', 'x') ||  \
      (tag) == MKTAG('A', 'V', 'i', 'n'))
 
 
diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 6e5142423b..10e883c923 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -1278,6 +1278,9 @@ static int mov_get_h264_codec_tag(AVFormatContext *s, MOVTrack *track)
                 else if (rate == 50) tag = MKTAG('a','i','1','5');
                 else if (rate == 60) tag = MKTAG('a','i','1','6');
             }
+        } else if (   track->enc->width == 4096 && track->enc->height == 2160
+                   || track->enc->width == 3840 && track->enc->height == 2160) {
+            tag = MKTAG('a','i','v','x');
         }
     }