Initialize a variable, and revalidate indexes when necessary....

source/patched-ffmpeg-mt/libavformat/oggdec.c

 /*
  * Ogg bitstream support
  * Luca Barbato <lu_zero@gentoo.org>
  * Based on tcvp implementation
  *
  */
 
 /**
     Copyright (C) 2005  Michael Ahlberg, Måns Rullgård
 
@@ skipping 592 matching lines @@
     av_free (ogg->streams);
     return 0;
 }
 
 
 static int64_t
 ogg_read_timestamp (AVFormatContext * s, int stream_index, int64_t * pos_arg,
                     int64_t pos_limit)
 {
     struct ogg *ogg = s->priv_data;
-    struct ogg_stream *os = ogg->streams + stream_index;
     ByteIOContext *bc = s->pb;
     int64_t pts = AV_NOPTS_VALUE;
-    int i;
+    int i = -1;
     int packet = 0;
     int64_t start_pos = *pos_arg;
     url_fseek(bc, *pos_arg, SEEK_SET);
     ogg_reset(ogg);
 
     while (url_ftell(bc) < pos_limit && !ogg_packet(s, &i, NULL, NULL, pos_arg)) {
         if (i == stream_index) {
+            struct ogg_stream *os = ogg->streams + stream_index;
             pts = ogg_calc_pts(s, i, NULL);
             if (os->keyframe_seek && !(os->pflags & AV_PKT_FLAG_KEY))
                 pts = AV_NOPTS_VALUE;
 
             // This is for the special case for the first packet in the stream.
             if (pts == AV_NOPTS_VALUE && start_pos <= s->data_offset && !packet) {
                 pts = 0;
             }
             ++packet;
         }
@@ skipping 14 matching lines @@
     int64_t seek_pts;
     int i;
 
     // Try seeking to a keyframe first. If this fails (very possible),
     // av_seek_frame will fall back to ignoring keyframes
     if (s->streams[stream_index]->codec->codec_type == AVMEDIA_TYPE_VIDEO
         && !(flags & AVSEEK_FLAG_ANY))
         os->keyframe_seek = 1;
 
     ret = av_seek_frame_binary(s, stream_index, timestamp, flags);
+    os = ogg->streams + stream_index;

[scherkus (not reviewing), 2011/02/26 00:42:27]

I'm lost as to what's changing streams/stream_index to force us to re-evaluate
os

     if (ret < 0)
         os->keyframe_seek = 0;
 
     // Save the position seeked to.
     pos_arg = seek_pos = url_ftell(s->pb);
     seek_pts = ogg_read_timestamp(s, stream_index, &pos_arg, url_fsize(s->pb));
+    os = ogg->streams + stream_index;

[scherkus (not reviewing), 2011/02/26 00:42:27]

ditto!

 
     // Since we have seeked to the beginning then reset lastpts and lastdts to 0.
     if (!seek_pts) {
         for (i = 0; i < ogg->nstreams; i++){
             struct ogg_stream *stream = ogg->streams + i;
             stream->lastpts = 0;
             stream->lastdts = 0;
         }
         os->keyframe_seek = 0;
     }
@@ skipping 17 matching lines @@
     sizeof (struct ogg),
     ogg_probe,
     ogg_read_header,
     ogg_read_packet,
     ogg_read_close,
     ogg_read_seek,
     ogg_read_timestamp,
     .extensions = "ogg",
     .flags = AVFMT_GENERIC_INDEX,
 };