diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index a9cf174af9..517d1ac152 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -22,7 +22,7 @@
 #define AVFORMAT_AVFORMAT_H
 
 #define LIBAVFORMAT_VERSION_MAJOR 52
-#define LIBAVFORMAT_VERSION_MINOR 84
+#define LIBAVFORMAT_VERSION_MINOR 85
 #define LIBAVFORMAT_VERSION_MICRO  0
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
@@ -245,6 +245,21 @@ void av_metadata_free(AVMetadata **m);
 int av_get_packet(ByteIOContext *s, AVPacket *pkt, int size);
 
 
+/**
+ * Reads data and appends it to the current content of the AVPacket.
+ * If pkt->size is 0 it behaves like av_get_packet.
+ * Note that this uses av_grow_packet and thus involves a realloc
+ * which is inefficient. Thus this function should only be used
+ * when there is no reasonable way to know (an upper bound of)
+ * the final size.
+ *
+ * @param pkt packet
+ * @param size amount of data to read
+ * @return >0 (read size) if OK, AVERROR_xxx otherwise, previous data
+ *         will not be lost even if an error occurs.
+ */
+int av_append_packet(ByteIOContext *s, AVPacket *pkt, int size);
+
 /*************************************************/
 /* fractional numbers for exact pts handling */
 
diff --git a/libavformat/utils.c b/libavformat/utils.c
index 937a615fc0..066da547f3 100644
--- a/libavformat/utils.c
+++ b/libavformat/utils.c
@@ -339,6 +339,21 @@ int av_get_packet(ByteIOContext *s, AVPacket *pkt, int size)
     return ret;
 }
 
+int av_append_packet(ByteIOContext *s, AVPacket *pkt, int size)
+{
+    int ret;
+    int old_size;
+    if (!pkt->size)
+        return av_get_packet(s, pkt, size);
+    old_size = pkt->size;
+    ret = av_grow_packet(pkt, size);
+    if (ret < 0)
+        return ret;
+    ret = get_buffer(s, pkt->data + old_size, size);
+    av_shrink_packet(pkt, old_size + FFMAX(ret, 0));
+    return ret;
+}
+
 
 int av_filename_number_test(const char *filename)
 {