qtdemux: Fix seeking on streams with frame reordering

The samples table is sorted by DTS, not PTS. As such we can only get the
correct result when using a binary search on it, if we search for the
DTS.
Also if we only ever search for the frame, where the following frame is
the first one with a PTS after the search position, we will generally
stop searching too early if frames are reordered.

In forwards playback this is not really a problem (after the decoder
reordered the frames, clipping is happening), in reverse playback
it means that we can output one or more frames too few as we stop too
early and the decoder would never receive it.

https://bugzilla.gnome.org/show_bug.cgi?id=782118

diff --git a/gst/isomp4/qtdemux.c b/gst/isomp4/qtdemux.c
index a6f870f..cadb544 100644 (file)
--- a/gst/isomp4/qtdemux.c
+++ b/gst/isomp4/qtdemux.c
@@ -1055,9 +1055,9 @@ typedef struct
 static gint
 find_func (QtDemuxSample * s1, gint64 * media_time, gpointer user_data)
 {
-  if ((gint64) s1->timestamp + s1->pts_offset > *media_time)
+  if ((gint64) s1->timestamp > *media_time)
     return 1;
-  if ((gint64) s1->timestamp + s1->pts_offset == *media_time)
+  if ((gint64) s1->timestamp == *media_time)
     return 0;
 
   return -1;
@@ -1066,7 +1066,7 @@ find_func (QtDemuxSample * s1, gint64 * media_time, gpointer user_data)
 /* find the index of the sample that includes the data for @media_time using a
  * binary search.  Only to be called in optimized cases of linear search below.
  *
- * Returns the index of the sample.
+ * Returns the index of the sample with the corresponding *DTS*.
  */
 static guint32
 gst_qtdemux_find_index (GstQTDemux * qtdemux, QtDemuxStream * str,
@@ -1156,20 +1156,31 @@ gst_qtdemux_find_index_linear (GstQTDemux * qtdemux, QtDemuxStream * str,
 
   /* use faster search if requested time in already parsed range */
   sample = str->samples + str->stbl_index;
-  if (str->stbl_index >= 0 &&
-      mov_time <= (sample->timestamp + sample->pts_offset))
-    return gst_qtdemux_find_index (qtdemux, str, media_time);
+  if (str->stbl_index >= 0 && mov_time <= sample->timestamp) {
+    index = gst_qtdemux_find_index (qtdemux, str, media_time);
+    sample = str->samples + index;
+  } else {
+    while (index < str->n_samples - 1) {
+      if (!qtdemux_parse_samples (qtdemux, str, index + 1))
+        goto parse_failed;
 
-  while (index < str->n_samples - 1) {
-    if (!qtdemux_parse_samples (qtdemux, str, index + 1))
-      goto parse_failed;
+      sample = str->samples + index + 1;
+      if (mov_time < sample->timestamp) {
+        sample = str->samples + index;
+        break;
+      }
 
-    sample = str->samples + index + 1;
-    if (mov_time < (sample->timestamp + sample->pts_offset))
-      break;
+      index++;
+    }
+  }
 
-    index++;
+  /* sample->timestamp is now <= media_time, need to find the corresponding
+   * PTS now by looking backwards */
+  while (index > 0 && sample->timestamp + sample->pts_offset > mov_time) {
+    index--;
+    sample = str->samples + index;
   }
+
   return index;
 
   /* ERRORS */