oggdec: resync from the last page.

Previously we re synced from where we where which cam lead
to loosing pages.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/oggdec.c

@@ -101,6 +101,7 @@ static int ogg_restore(AVFormatContext *s, int discard)
             av_free(ogg->streams[i].buf);
 
         avio_seek(bc, ost->pos, SEEK_SET);
+        ogg->page_pos = -1;
         ogg->curidx   = ost->curidx;
         ogg->nstreams = ost->nstreams;
         ogg->streams  = av_realloc(ogg->streams,
@@ -145,6 +146,7 @@ static int ogg_reset(AVFormatContext *s)
         }
     }
 
+    ogg->page_pos = -1;
     ogg->curidx = -1;
 
     return 0;
@@ -296,6 +298,12 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
             sync[(sp + 2) & 3] == 'g' && sync[(sp + 3) & 3] == 'S')
             break;
 
+        if(!i && bc->seekable && ogg->page_pos > 0) {
+            memset(sync, 0, 4);
+            avio_seek(bc, ogg->page_pos+4, SEEK_SET);
+            ogg->page_pos = -1;
+        }
+
         c = avio_r8(bc);
 
         if (url_feof(bc))
@@ -334,6 +342,7 @@ static int ogg_read_page(AVFormatContext *s, int *sid)
     }
 
     os = ogg->streams + idx;
+    ogg->page_pos =
     os->page_pos = avio_tell(bc) - 27;
 
     if (os->psize > 0)
@@ -558,6 +567,7 @@ static int ogg_get_length(AVFormatContext *s)
 
     ogg_save(s);
     avio_seek(s->pb, end, SEEK_SET);
+    ogg->page_pos = -1;
 
     while (!ogg_read_page(s, &i)) {
         if (ogg->streams[i].granule != -1 && ogg->streams[i].granule != 0 &&

libavformat/oggdec.h

@@ -100,6 +100,7 @@ struct ogg {
     int nstreams;
     int headers;
     int curidx;
+    int64_t page_pos;                   ///< file offset of the current page
     struct ogg_state *state;
 };