diff --git a/gst/isomp4/atoms.c b/gst/isomp4/atoms.c
index 4ac7670..c300e67 100644
--- a/gst/isomp4/atoms.c
+++ b/gst/isomp4/atoms.c
@@ -1132,6 +1132,20 @@
     atom_info_list_free (udta->entries);
 }
 
+/* Clear added tags, but keep the context/flavor the same */
+void
+atom_udta_clear_tags (AtomUDTA * udta)
+{
+  if (udta->entries) {
+    atom_info_list_free (udta->entries);
+    udta->entries = NULL;
+  }
+  if (udta->meta && udta->meta->ilst->entries) {
+    atom_info_list_free (udta->meta->ilst->entries);
+    udta->meta->ilst->entries = NULL;
+  }
+}
+
 static void
 atom_tag_data_init (AtomTagData * data)
 {
@@ -1980,12 +1994,13 @@
   prop_copy_ensure_buffer (buffer, size, offset,
       8 * atom_array_get_len (&stco64->entries));
   for (i = 0; i < atom_array_get_len (&stco64->entries); i++) {
-    guint64 *value = &atom_array_index (&stco64->entries, i);
+    guint64 value =
+        atom_array_index (&stco64->entries, i) + stco64->chunk_offset;
 
     if (trunc_to_32) {
-      prop_copy_uint32 ((guint32) * value, buffer, size, offset);
+      prop_copy_uint32 ((guint32) value, buffer, size, offset);
     } else {
-      prop_copy_uint64 (*value, buffer, size, offset);
+      prop_copy_uint64 (value, buffer, size, offset);
     }
   }
 
@@ -2749,6 +2764,12 @@
   atom_moov_add_trex (moov, atom_trex_new (trak));
 }
 
+guint
+atom_moov_get_trak_count (AtomMOOV * moov)
+{
+  return g_list_length (moov->traks);
+}
+
 static guint64
 atom_trak_get_duration (AtomTRAK * trak)
 {
@@ -2821,28 +2842,27 @@
 }
 
 void
-atom_stco64_chunks_add_offset (AtomSTCO64 * stco64, guint32 offset)
+atom_stco64_chunks_set_offset (AtomSTCO64 * stco64, guint32 offset)
 {
-  guint i;
-
-  for (i = 0; i < atom_array_get_len (&stco64->entries); i++) {
-    guint64 *value = &atom_array_index (&stco64->entries, i);
-
-    *value += offset;
-  }
+  stco64->chunk_offset = offset;
 }
 
 void
-atom_moov_chunks_add_offset (AtomMOOV * moov, guint32 offset)
+atom_moov_chunks_set_offset (AtomMOOV * moov, guint32 offset)
 {
   GList *traks = moov->traks;
 
+  if (offset == moov->chunks_offset)
+    return;                     /* Nothing to do */
+
   while (traks) {
     AtomTRAK *trak = (AtomTRAK *) traks->data;
 
-    atom_stco64_chunks_add_offset (&trak->mdia.minf.stbl.stco64, offset);
+    atom_stco64_chunks_set_offset (&trak->mdia.minf.stbl.stco64, offset);
     traks = g_list_next (traks);
   }
+
+  moov->chunks_offset = offset;
 }
 
 void