Write segment UID

Originally committed as revision 10337 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/matroskaenc.c

@@ -20,6 +20,7 @@
  */
 
 #include "avformat.h"
+#include "random.h"
 #include "riff.h"
 #include "xiph.h"
 #include "matroska.h"
@@ -61,6 +62,8 @@ typedef struct MatroskaMuxContext {
     mkv_seekhead    *main_seekhead;
     mkv_seekhead    *cluster_seekhead;
     mkv_cues        *cues;
+
+    AVRandomState   rand_state;
 } MatroskaMuxContext;
 
 static void put_ebml_id(ByteIOContext *pb, unsigned int id)
@@ -507,6 +510,9 @@ static int mkv_write_header(AVFormatContext *s)
     MatroskaMuxContext *mkv = s->priv_data;
     ByteIOContext *pb = &s->pb;
     offset_t ebml_header, segment_info;
+    int i;
+
+    av_init_random(av_gettime(), &mkv->rand_state);
 
     ebml_header = start_ebml_master(pb, EBML_ID_HEADER);
     put_ebml_uint   (pb, EBML_ID_EBMLVERSION        ,           1);
@@ -536,11 +542,16 @@ static int mkv_write_header(AVFormatContext *s)
     if (strlen(s->title))
         put_ebml_string(pb, MATROSKA_ID_TITLE, s->title);
     if (!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {
+        uint8_t segmentuid[16];
+        for (i = 0; i < 16; i++)
+            segmentuid[i] = av_random(&mkv->rand_state);
+
         put_ebml_string(pb, MATROSKA_ID_MUXINGAPP , LIBAVFORMAT_IDENT);
         put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, LIBAVFORMAT_IDENT);
         put_ebml_date  (pb, MATROSKA_ID_DATEUTC   , av_gettime()     );
+        put_ebml_binary(pb, MATROSKA_ID_SEGMENTUID, segmentuid,    16);
     }
-    // XXX: segment UID
+
     // reserve space for the duration
     mkv->duration = 0;
     mkv->duration_offset = url_ftell(pb);