oggdemux: implement keyframe seeking

Implement keyframe seeking in oggdemux by doing the double seek trick. First
seek to the required position, then read pages for all streams to grab the
granulepos (to know the timing of the keyframe) of each stream, then seek back
to the first keyframe.

ext/ogg/gstoggdemux.c

@@ -140,6 +140,7 @@ gst_ogg_pad_init (GstOggPad * pad)
   pad->mode = GST_OGG_PAD_MODE_INIT;
 
   pad->current_granule = -1;
+  pad->keyframe_granule = -1;
 
   pad->start_time = GST_CLOCK_TIME_NONE;
 
@@ -356,6 +357,7 @@ gst_ogg_pad_reset (GstOggPad * pad)
   pad->last_ret = GST_FLOW_OK;
   pad->last_stop = GST_CLOCK_TIME_NONE;
   pad->current_granule = -1;
+  pad->keyframe_granule = -1;
 }
 
 /* called when the skeleton fishead is found. Caller ensures the packet is
@@ -1601,63 +1603,17 @@ gst_ogg_demux_activate_chain (GstOggDemux * ogg, GstOggChain * chain,
   return TRUE;
 }
 
-/* 
- * do seek to time @position, return FALSE or chain and TRUE
- */
 static gboolean
-gst_ogg_demux_do_seek (GstOggDemux * ogg, GstSegment * segment,
+do_binary_search (GstOggDemux * ogg, GstOggChain * chain, gint64 begin,
-    gboolean accurate, GstOggChain ** rchain)
+    gint64 end, gint64 begintime, gint64 endtime, gint64 target,
+    gint64 * offset)
 {
-  guint64 position;
-  GstOggChain *chain = NULL;
-  gint64 begin, end;
-  gint64 begintime, endtime;
-  gint64 target;
   gint64 best;
-  gint64 total;
-  gint64 result = 0;
   GstFlowReturn ret;
-  gint i;
+  gint64 result = 0;
 
-  position = segment->last_stop;
-
-  /* first find the chain to search in */
-  total = ogg->total_time;
-  if (ogg->chains->len == 0)
-    goto no_chains;
-
-  for (i = ogg->chains->len - 1; i >= 0; i--) {
-    chain = g_array_index (ogg->chains, GstOggChain *, i);
-    total -= chain->total_time;
-    if (position >= total)
-      break;
-  }
-
-  begin = chain->offset;
-  end = chain->end_offset;
-  begintime = chain->begin_time;
-  endtime = begintime + chain->total_time;
-  target = position - total + begintime;
-  if (accurate) {
-    if (segment->rate > 0.0) {
-      /* FIXME, seek 2 seconds early to catch keyframes, better implement
-       * keyframe detection. */
-      if (target - 2 * GST_SECOND > begintime)
-        target = target - (gint64) 2 *GST_SECOND;
-      else
-        target = begintime;
-    } else {
-      if (target + GST_SECOND < endtime)
-        target = target + (gint64) GST_SECOND;
-      else
-        target = endtime;
-    }
-  }
   best = begin;
 
-  GST_DEBUG_OBJECT (ogg,
-      "seeking to %" GST_TIME_FORMAT " in chain %p",
-      GST_TIME_ARGS (position), chain);
   GST_DEBUG_OBJECT (ogg,
       "chain offset %" G_GINT64_FORMAT ", end offset %" G_GINT64_FORMAT, begin,
       end);
@@ -1715,6 +1671,7 @@ gst_ogg_demux_do_seek (GstOggDemux * ogg, GstSegment * segment,
         GstClockTime granuletime;
         GstOggPad *pad;
 
+        /* get the granulepos */
         GST_LOG_OBJECT (ogg, "found next ogg page at %" G_GINT64_FORMAT,
             result);
         granulepos = ogg_page_granulepos (&og);
@@ -1723,14 +1680,17 @@ gst_ogg_demux_do_seek (GstOggDemux * ogg, GstSegment * segment,
           continue;
         }
 
+        /* get the stream */
         pad = gst_ogg_chain_get_stream (chain, ogg_page_serialno (&og));
         if (pad == NULL || pad->map.is_skeleton)
           continue;
 
+        /* convert granulepos to time */
         granuletime = gst_ogg_stream_get_end_time_for_granulepos (&pad->map,
             granulepos);
         if (granuletime < pad->start_time)
           continue;
+
         GST_LOG_OBJECT (ogg, "granulepos %" G_GINT64_FORMAT " maps to time %"
             GST_TIME_FORMAT, granulepos, GST_TIME_ARGS (granuletime));
 
@@ -1745,8 +1705,10 @@ gst_ogg_demux_do_seek (GstOggDemux * ogg, GstSegment * segment,
           begin = ogg->offset;  /* raw offset of next page */
           begintime = granuletime;
 
+          /*
              if (target - begintime > GST_SECOND)
              break;
+           */
 
           bisect = begin;       /* *not* begin + 1 */
         } else {
@@ -1770,9 +1732,139 @@ gst_ogg_demux_do_seek (GstOggDemux * ogg, GstSegment * segment,
         goto seek_error;
     }
   }
-
   GST_DEBUG_OBJECT (ogg, "seeking to %" G_GINT64_FORMAT, best);
   gst_ogg_demux_seek (ogg, best);
+  *offset = best;
+
+  return TRUE;
+
+  /* ERRORS */
+seek_error:
+  {
+    GST_DEBUG_OBJECT (ogg, "got a seek error");
+    return FALSE;
+  }
+}
+
+/*
+ * do seek to time @position, return FALSE or chain and TRUE
+ */
+static gboolean
+gst_ogg_demux_do_seek (GstOggDemux * ogg, GstSegment * segment,
+    gboolean accurate, gboolean keyframe, GstOggChain ** rchain)
+{
+  guint64 position;
+  GstOggChain *chain = NULL;
+  gint64 begin, end;
+  gint64 begintime, endtime;
+  gint64 target;
+  gint64 best;
+  gint64 total;
+  gint64 result = 0;
+  GstFlowReturn ret;
+  gint i, pending, len;
+
+  position = segment->last_stop;
+
+  /* first find the chain to search in */
+  total = ogg->total_time;
+  if (ogg->chains->len == 0)
+    goto no_chains;
+
+  for (i = ogg->chains->len - 1; i >= 0; i--) {
+    chain = g_array_index (ogg->chains, GstOggChain *, i);
+    total -= chain->total_time;
+    if (position >= total)
+      break;
+  }
+
+  /* first step, locate page containing the required data */
+  begin = chain->offset;
+  end = chain->end_offset;
+  begintime = chain->begin_time;
+  endtime = begintime + chain->total_time;
+  target = position - total + begintime;
+
+  if (!do_binary_search (ogg, chain, begin, end, begintime, endtime, target,
+          &best))
+    goto seek_error;
+
+  /* second step: find pages for all streams, we use the keyframe_granule to keep
+   * track of which ones we saw. If we have seen a page for each stream we can
+   * calculate the positions of each keyframe. */
+  GST_DEBUG_OBJECT (ogg, "find keyframes");
+  len = pending = chain->streams->len;
+
+  while (TRUE) {
+    ogg_page og;
+    gint64 granulepos;
+    GstOggPad *pad;
+
+    ret = gst_ogg_demux_get_next_page (ogg, &og, end - ogg->offset, &result);
+    GST_LOG_OBJECT (ogg, "looking for next page returned %" G_GINT64_FORMAT,
+        result);
+    if (ret == GST_FLOW_LIMIT) {
+      GST_LOG_OBJECT (ogg, "reached limit");
+      break;
+    }
+
+    /* get the stream */
+    pad = gst_ogg_chain_get_stream (chain, ogg_page_serialno (&og));
+    if (pad == NULL)
+      continue;
+
+    if (pad->map.is_skeleton)
+      goto next;
+
+    /* we've seen this pad */
+    if (pad->keyframe_granule != -1)
+      continue;
+
+    granulepos = ogg_page_granulepos (&og);
+    if (granulepos == -1) {
+      GST_LOG_OBJECT (ogg, "granulepos of next page is -1");
+      continue;
+    }
+
+    /* store granule of this pad */
+    pad->keyframe_granule = gst_ogg_stream_granulepos_to_key_granule (&pad->map,
+        granulepos);
+    GST_LOG_OBJECT (ogg, "marking stream granule %" G_GINT64_FORMAT,
+        pad->keyframe_granule);
+
+  next:
+    pending--;
+    if (pending == 0)
+      break;
+  }
+
+  /* figure out where the keyframes are */
+  for (i = 0; i < chain->streams->len; i++) {
+    GstOggPad *pad = g_array_index (chain->streams, GstOggPad *, i);
+    GstClockTime granuletime;
+
+    granuletime =
+        gst_ogg_stream_granule_to_time (&pad->map, pad->keyframe_granule);
+    GST_LOG_OBJECT (ogg, "stream %08x granule time %" GST_TIME_FORMAT,
+        pad->map.serialno, GST_TIME_ARGS (granuletime));
+
+    if (granuletime != -1 && granuletime < target)
+      target = granuletime;
+  }
+
+  GST_LOG_OBJECT (ogg, "final seek to target %" GST_TIME_FORMAT,
+      GST_TIME_ARGS (target));
+
+  /* last step, seek to the location of the keyframe */
+  if (!do_binary_search (ogg, chain, begin, end, begintime, endtime, target,
+          &best))
+    goto seek_error;
+
+  if (keyframe) {
+    segment->time = target;
+    segment->last_stop = target - begintime;
+  }
+
   *rchain = chain;
 
   return TRUE;
@@ -1795,7 +1887,7 @@ gst_ogg_demux_perform_seek (GstOggDemux * ogg, GstEvent * event)
 {
   GstOggChain *chain = NULL;
   gboolean res;
-  gboolean flush, accurate;
+  gboolean flush, accurate, keyframe;
   GstFormat format;
   gdouble rate;
   GstSeekFlags flags;
@@ -1829,6 +1921,7 @@ gst_ogg_demux_perform_seek (GstOggDemux * ogg, GstEvent * event)
 
   flush = flags & GST_SEEK_FLAG_FLUSH;
   accurate = flags & GST_SEEK_FLAG_ACCURATE;
+  keyframe = flags & GST_SEEK_FLAG_KEY_UNIT;
 
   /* first step is to unlock the streaming thread if it is
    * blocked in a chain call, we do this by starting the flush. because
@@ -1917,7 +2010,7 @@ gst_ogg_demux_perform_seek (GstOggDemux * ogg, GstEvent * event)
   }
 
   /* for reverse we will already seek accurately */
-  res = gst_ogg_demux_do_seek (ogg, &ogg->segment, accurate, &chain);
+  res = gst_ogg_demux_do_seek (ogg, &ogg->segment, accurate, keyframe, &chain);
 
   /* seek failed, make sure we continue the current chain */
   if (!res) {