mp3enc: add an option for disabling the Xing frame.

doc/muxers.texi

@@ -437,9 +437,10 @@ optionally an ID3v1 tag at the end. ID3v2.3 and ID3v2.4 are supported, the
 @code{id3v2_version} option controls which one is used. The legacy ID3v1 tag is
 not written by default, but may be enabled with the @code{write_id3v1} option.
 
-For seekable output the muxer also writes a Xing frame at the beginning, which
-contains the number of frames in the file. It is useful for computing duration
-of VBR files.
+The muxer may also write a Xing frame at the beginning, which contains the
+number of frames in the file. It is useful for computing duration of VBR files.
+The Xing frame is written if the output stream is seekable and if the
+@code{write_xing} option is set to 1 (the default).
 
 The muxer supports writing ID3v2 attached pictures (APIC frames). The pictures
 are supplied to the muxer in form of a video stream with a single packet. There

libavformat/mp3enc.c

@@ -84,6 +84,7 @@ typedef struct MP3Context {
     ID3v2EncContext id3;
     int id3v2_version;
     int write_id3v1;
+    int write_xing;
 
     /* xing header */
     int64_t xing_offset;
@@ -121,7 +122,7 @@ static void mp3_write_xing(AVFormatContext *s)
     int xing_offset;
     int ver = 0;
 
-    if (!s->pb->seekable)
+    if (!s->pb->seekable || !mp3->write_xing)
         return;
 
     for (i = 0; i < FF_ARRAY_ELEMS(avpriv_mpa_freq_tab); i++) {
@@ -321,6 +322,8 @@ static const AVOption options[] = {
       offsetof(MP3Context, id3v2_version), AV_OPT_TYPE_INT, {.i64 = 4}, 3, 4, AV_OPT_FLAG_ENCODING_PARAM},
     { "write_id3v1", "Enable ID3v1 writing. ID3v1 tags are written in UTF-8 which may not be supported by most software.",
       offsetof(MP3Context, write_id3v1), AV_OPT_TYPE_INT, {.i64 = 0}, 0, 1, AV_OPT_FLAG_ENCODING_PARAM},
+    { "write_xing",  "Write the Xing header containing file duration.",
+      offsetof(MP3Context, write_xing),  AV_OPT_TYPE_INT, {.i64 = 1}, 0, 1, AV_OPT_FLAG_ENCODING_PARAM},
     { NULL },
 };