matroska: move LFG state from muxer context to local variable

The LFG is only used in one place, so there is no need to keep it in
the context.

Originally committed as revision 23527 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/matroskaenc.c

@@ -83,7 +83,6 @@ typedef struct MatroskaMuxContext {
     mkv_cues        *cues;
     mkv_track       *tracks;
 
-    AVLFG           lfg;
     unsigned int    audio_buffer_size;
     AVPacket        cur_audio_pkt;
 } MatroskaMuxContext;
@@ -699,8 +698,6 @@ static int mkv_write_header(AVFormatContext *s)
     if (!strcmp(s->oformat->name, "webm")) mkv->mode = MODE_WEBM;
     else                                   mkv->mode = MODE_MATROSKAv2;
 
-    av_lfg_init(&mkv->lfg, av_get_random_seed());
-
     mkv->tracks = av_mallocz(s->nb_streams * sizeof(*mkv->tracks));
     if (!mkv->tracks)
         return AVERROR(ENOMEM);
@@ -736,8 +733,12 @@ static int mkv_write_header(AVFormatContext *s)
         put_ebml_string(pb, MATROSKA_ID_TITLE, tag->value);
     if (!(s->streams[0]->codec->flags & CODEC_FLAG_BITEXACT)) {
         uint32_t segment_uid[4];
+        AVLFG lfg;
+
+        av_lfg_init(&lfg, av_get_random_seed());
+
         for (i = 0; i < 4; i++)
-            segment_uid[i] = av_lfg_get(&mkv->lfg);
+            segment_uid[i] = av_lfg_get(&lfg);
 
         put_ebml_string(pb, MATROSKA_ID_MUXINGAPP , LIBAVFORMAT_IDENT);
         put_ebml_string(pb, MATROSKA_ID_WRITINGAPP, LIBAVFORMAT_IDENT);