diff --git a/libavformat/avio.h b/libavformat/avio.h
index 6f4ed8440d..525eb7129e 100644
--- a/libavformat/avio.h
+++ b/libavformat/avio.h
@@ -327,6 +327,8 @@ typedef struct AVIOContext {
      * This is current internal only, do not use from outside.
      */
     int (*short_seek_get)(void *opaque);
+
+    int64_t written;
 } AVIOContext;
 
 /**
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index ef6a0d4e9b..0a7c39eacd 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -120,6 +120,7 @@ int ffio_init_context(AVIOContext *s,
     s->current_type          = AVIO_DATA_MARKER_UNKNOWN;
     s->last_time             = AV_NOPTS_VALUE;
     s->short_seek_get        = NULL;
+    s->written               = 0;
 
     return 0;
 }
@@ -154,6 +155,9 @@ static void writeout(AVIOContext *s, const uint8_t *data, int len)
             ret = s->write_packet(s->opaque, (uint8_t *)data, len);
         if (ret < 0) {
             s->error = ret;
+        } else {
+            if (s->pos + len > s->written)
+                s->written = s->pos + len;
         }
     }
     if (s->current_type == AVIO_DATA_MARKER_SYNC_POINT ||
@@ -323,6 +327,9 @@ int64_t avio_size(AVIOContext *s)
     if (!s)
         return AVERROR(EINVAL);
 
+    if (s->written)
+        return s->written;
+
     if (!s->seek)
         return AVERROR(ENOSYS);
     size = s->seek(s->opaque, 0, AVSEEK_SIZE);
diff --git a/libavformat/version.h b/libavformat/version.h
index 0920b48145..411fd6613d 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -33,7 +33,7 @@
 // Also please add any ticket numbers that you believe might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  57
 #define LIBAVFORMAT_VERSION_MINOR  72
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \