diff --git a/libavformat/asf.c b/libavformat/asf.c
index 58e17e9cef..e6659923d7 100644
--- a/libavformat/asf.c
+++ b/libavformat/asf.c
@@ -156,20 +156,3 @@ const AVMetadataConv ff_asf_metadata_conv[] = {
 //  { "Year"               , "date"        }, TODO: conversion year<->date
     { 0 }
 };
-
-int ff_put_str16_nolen(ByteIOContext *s, const char *tag)
-{
-    const uint8_t *q = tag;
-    int ret = 0;
-
-    while (*q) {
-        uint32_t ch;
-        uint16_t tmp;
-
-        GET_UTF8(ch, *q++, break;)
-        PUT_UTF16(ch, tmp, put_le16(s, tmp);ret += 2;)
-    }
-    put_le16(s, 0);
-    ret += 2;
-    return ret;
-}
diff --git a/libavformat/asf.h b/libavformat/asf.h
index f3705e946a..8cf517dd14 100644
--- a/libavformat/asf.h
+++ b/libavformat/asf.h
@@ -230,7 +230,6 @@ extern const AVMetadataConv ff_asf_metadata_conv[];
 #define ASF_PL_FLAG_KEY_FRAME 0x80 //1000 0000
 
 extern AVInputFormat asf_demuxer;
-int ff_put_str16_nolen(ByteIOContext *s, const char *tag);
 int ff_guidcmp(const void *g1, const void *g2);
 void ff_get_guid(ByteIOContext *s, ff_asf_guid *g);
 
diff --git a/libavformat/asfenc.c b/libavformat/asfenc.c
index b964953b2b..0c2a6ae94a 100644
--- a/libavformat/asfenc.c
+++ b/libavformat/asfenc.c
@@ -211,7 +211,7 @@ static void put_str16(ByteIOContext *s, const char *tag)
     if (url_open_dyn_buf(&dyn_buf) < 0)
         return;
 
-    ff_put_str16_nolen(dyn_buf, tag);
+    avio_put_str16le(dyn_buf, tag);
     len = url_close_dyn_buf(dyn_buf, &pb);
     put_le16(s, len);
     put_buffer(s, pb, len);
@@ -346,7 +346,7 @@ static int asf_write_header1(AVFormatContext *s, int64_t file_size, int64_t data
         hpos = put_header(pb, &ff_asf_comment_header);
 
         for (n = 0; n < FF_ARRAY_ELEMS(tags); n++) {
-            len = tags[n] ? ff_put_str16_nolen(dyn_buf, tags[n]->value) : 0;
+            len = tags[n] ? avio_put_str16le(dyn_buf, tags[n]->value) : 0;
             put_le16(pb, len);
         }
         len = url_close_dyn_buf(dyn_buf, &buf);
@@ -474,7 +474,7 @@ static int asf_write_header1(AVFormatContext *s, int64_t file_size, int64_t data
         if ( url_open_dyn_buf(&dyn_buf) < 0)
             return AVERROR(ENOMEM);
 
-        ff_put_str16_nolen(dyn_buf, desc);
+        avio_put_str16le(dyn_buf, desc);
         len = url_close_dyn_buf(dyn_buf, &buf);
         put_le16(pb, len / 2); // "number of characters" = length in bytes / 2
 
diff --git a/libavformat/avio.h b/libavformat/avio.h
index 9f71c1921e..b35d4c716c 100644
--- a/libavformat/avio.h
+++ b/libavformat/avio.h
@@ -377,6 +377,12 @@ attribute_deprecated void put_strz(ByteIOContext *s, const char *buf);
  */
 int avio_put_str(ByteIOContext *s, const char *str);
 
+/**
+ * Convert an UTF-8 string to UTF-16LE and write it.
+ * @return number of bytes written.
+ */
+int avio_put_str16le(ByteIOContext *s, const char *str);
+
 /**
  * fseek() equivalent for ByteIOContext.
  * @return new position or AVERROR.
diff --git a/libavformat/aviobuf.c b/libavformat/aviobuf.c
index 4f0c16c308..5aeced1b9f 100644
--- a/libavformat/aviobuf.c
+++ b/libavformat/aviobuf.c
@@ -283,6 +283,23 @@ int avio_put_str(ByteIOContext *s, const char *str)
     return len;
 }
 
+int avio_put_str16le(ByteIOContext *s, const char *str)
+{
+    const uint8_t *q = str;
+    int ret = 0;
+
+    while (*q) {
+        uint32_t ch;
+        uint16_t tmp;
+
+        GET_UTF8(ch, *q++, break;)
+        PUT_UTF16(ch, tmp, put_le16(s, tmp);ret += 2;)
+    }
+    put_le16(s, 0);
+    ret += 2;
+    return ret;
+}
+
 int ff_get_v_length(uint64_t val){
     int i=1;
 
diff --git a/libavformat/mmst.c b/libavformat/mmst.c
index 57cca5d0d4..08e3b3e660 100644
--- a/libavformat/mmst.c
+++ b/libavformat/mmst.c
@@ -34,7 +34,6 @@
 #include "libavutil/intreadwrite.h"
 #include "libavcodec/bytestream.h"
 #include "network.h"
-#include "asf.h"
 
 #define LOCAL_ADDRESS 0xc0a80081    // FIXME get and use correct local ip address.
 #define LOCAL_PORT    1037          // as above.
@@ -159,7 +158,7 @@ static void mms_put_utf16(MMSContext *mms, uint8_t *src)
     init_put_byte(&bic, mms->write_out_ptr,
             sizeof(mms->out_buffer) - size, 1, NULL, NULL, NULL, NULL);
 
-    len = ff_put_str16_nolen(&bic, src);
+    len = avio_put_str16le(&bic, src);
     mms->write_out_ptr += len;
 }