@@ -275,6 +275,8 @@ typedef struct OptionsContext {

     SpecifierOpt *ts_scale;

     int        nb_ts_scale;

+    SpecifierOpt *dump_attachment;

+    int        nb_dump_attachment;

     /* output options */

     StreamMap *stream_maps;

@@ -2843,6 +2845,60 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)

     }

 }

+static void assert_file_overwrite(const char *filename)

+{

+    if (!file_overwrite &&

+        (strchr(filename, ':') == NULL || filename[1] == ':' ||

+         av_strstart(filename, "file:", NULL))) {

+        if (avio_check(filename, 0) == 0) {

+            if (!using_stdin) {

+                fprintf(stderr,"File '%s' already exists. Overwrite ? [y/N] ", filename);

+                fflush(stderr);

+                if (!read_yesno()) {

+                    fprintf(stderr, "Not overwriting - exiting\n");

+                    exit_program(1);

+                }

+            }

+            else {

+                fprintf(stderr,"File '%s' already exists. Exiting.\n", filename);

+                exit_program(1);

+            }

+        }

+    }

+}

+

+static void dump_attachment(AVStream *st, const char *filename)

+{

+    int ret;

+    AVIOContext *out = NULL;

+    AVDictionaryEntry *e;

+

+    if (!st->codec->extradata_size) {

+        av_log(NULL, AV_LOG_WARNING, "No extradata to dump in stream #%d:%d.\n",

+               nb_input_files - 1, st->index);

+        return;

+    }

+    if (!*filename && (e = av_dict_get(st->metadata, "filename", NULL, 0)))

+        filename = e->value;

+    if (!*filename) {

+        av_log(NULL, AV_LOG_FATAL, "No filename specified and no 'filename' tag"

+               "in stream #%d:%d.\n", nb_input_files - 1, st->index);

+        exit_program(1);

+    }

+

+    assert_file_overwrite(filename);

+

+    if ((ret = avio_open (&out, filename, AVIO_FLAG_WRITE)) < 0) {

+        av_log(NULL, AV_LOG_FATAL, "Could not open file %s for writing.\n",

+               filename);

+        exit_program(1);

+    }

+

+    avio_write(out, st->codec->extradata, st->codec->extradata_size);

+    avio_flush(out);

+    avio_close(out);

+}

+

 static int opt_input_file(OptionsContext *o, const char *opt, const char *filename)

 {

     AVFormatContext *ic;

@@ -2943,6 +2999,17 @@ static int opt_input_file(OptionsContext *o, const char *opt, const char *filena

     input_files[nb_input_files - 1].nb_streams = ic->nb_streams;

     input_files[nb_input_files - 1].rate_emu   = o->rate_emu;

+    for (i = 0; i < o->nb_dump_attachment; i++) {

+        int j;

+

+        for (j = 0; j < ic->nb_streams; j++) {

+            AVStream *st = ic->streams[j];

+

+            if (check_stream_specifier(ic, st, o->dump_attachment[i].specifier) == 1)

+                dump_attachment(st, o->dump_attachment[i].u.str);

+        }

+    }

+

     for (i = 0; i < orig_nb_streams; i++)

         av_dict_free(&opts[i]);

     av_freep(&opts);

@@ -3602,25 +3669,7 @@ static void opt_output_file(void *optctx, const char *filename)

     if (!(oc->oformat->flags & AVFMT_NOFILE)) {

         /* test if it already exists to avoid loosing precious files */

-        if (!file_overwrite &&

-            (strchr(filename, ':') == NULL ||

-             filename[1] == ':' ||

-             av_strstart(filename, "file:", NULL))) {

-            if (avio_check(filename, 0) == 0) {

-                if (!using_stdin) {

-                    fprintf(stderr,"File '%s' already exists. Overwrite ? [y/N] ", filename);

-                    fflush(stderr);

-                    if (!read_yesno()) {

-                        fprintf(stderr, "Not overwriting - exiting\n");

-                        exit_program(1);

-                    }

-                }

-                else {

-                    fprintf(stderr,"File '%s' already exists. Exiting.\n", filename);

-                    exit_program(1);

-                }

-            }

-        }

+        assert_file_overwrite(filename);

         /* open the file */

         if ((err = avio_open(&oc->pb, filename, AVIO_FLAG_WRITE)) < 0) {

@@ -4086,6 +4135,7 @@ static const OptionDef options[] = {

 #endif

     { "stats", OPT_BOOL, {&print_stats}, "print progress report during encoding", },

     { "attach", HAS_ARG | OPT_FUNC2, {(void*)opt_attach}, "add an attachment to the output file", "filename" },

+    { "dump_attachment", HAS_ARG | OPT_STRING | OPT_SPEC, {.off = OFFSET(dump_attachment)}, "extract an attachment into a file", "filename" },

     /* video options */

     { "vframes", HAS_ARG | OPT_VIDEO | OPT_FUNC2, {(void*)opt_video_frames}, "set the number of video frames to record", "number" },

@@ -207,6 +207,24 @@ avconv -i INPUT -attach DejaVuSans.ttf -metadata:s:2 mimetype=application/x-true

 @end example

 (assuming that the attachment stream will be third in the output file).

+@item -dump_attachment[:@var{stream_specifier}] @var{filename} (@emph{input,per-stream})

+Extract the matching attachment stream into a file named @var{filename}. If

+@var{filename} is empty, then the value of the @code{filename} metadata tag

+will be used.

+

+E.g. to extract the first attachment to a file named 'out.ttf':

+@example

+avconv -dump_attachment:t:0 out.ttf INPUT

+@end example

+To extract all attachments to files determined by the @code{filename} tag:

+@example

+avconv -dump_attachment:t "" INPUT

+@end example

+

+Technical note -- attachments are implemented as codec extradata, so this

+option can actually be used to extract extradata from any stream, not just

+attachments.

+

 @end table

 @section Video Options