diff --git a/code/fcpxml/writer/core.py b/code/fcpxml/writer/core.py
index 932e2df..57243a9 100644
--- a/code/fcpxml/writer/core.py
+++ b/code/fcpxml/writer/core.py
@@ -97,6 +97,8 @@ class ModifierCore:
         self.fps = self._detect_fps()
         # Lazily filled on the first generated title; see _unique_text_style_id.
         self._text_style_ids: Optional[set] = None
+        # Lazily filled on the first clip split/cut; see _unique_tracking_shape_id.
+        self._tracking_shape_ids: Optional[set] = None
         self._build_resource_index()
         self._build_clip_index()
 
diff --git a/code/fcpxml/writer/cut.py b/code/fcpxml/writer/cut.py
index 0f86c31..29ff1d6 100644
--- a/code/fcpxml/writer/cut.py
+++ b/code/fcpxml/writer/cut.py
@@ -125,6 +125,7 @@ class CutMixin:
                 new_clip, current_start, segment_duration
             )
             self._reassign_text_style_ids(new_clip)
+            self._reassign_tracking_shape_ids(new_clip)
 
             spine.insert(clip_index + len(new_clips), new_clip)
             new_clips.append(new_clip)
@@ -243,6 +244,7 @@ class CutMixin:
             new_clip.set('duration', seg_duration.to_fcpxml())
             self._filter_children_for_segment(new_clip, seg_start, seg_duration)
             self._reassign_text_style_ids(new_clip)
+            self._reassign_tracking_shape_ids(new_clip)
             spine.insert(clip_index + len(new_clips), new_clip)
             new_clips.append(new_clip)
             current_offset = current_offset + seg_duration
diff --git a/code/fcpxml/writer/titles.py b/code/fcpxml/writer/titles.py
index 4732e88..1cb1c3f 100644
--- a/code/fcpxml/writer/titles.py
+++ b/code/fcpxml/writer/titles.py
@@ -164,6 +164,44 @@ class TitlesMixin:
             for ref_el in clip.findall(f".//text-style[@ref='{old_id}']"):
                 ref_el.set('ref', new_id)
 
+    def _unique_tracking_shape_id(self, base: str) -> str:
+        """Return a document-unique ``id`` for a ``<tracking-shape>``."""
+        stem = base or "tr"
+        if self._tracking_shape_ids is None:
+            self._tracking_shape_ids = {
+                ts.get('id') for ts in self.root.findall('.//tracking-shape')
+            }
+        candidate = f"{stem}_0"
+        counter = 0
+        while candidate in self._tracking_shape_ids:
+            counter += 1
+            candidate = f"{stem}_{counter}"
+        self._tracking_shape_ids.add(candidate)
+        return candidate
+
+    def _reassign_tracking_shape_ids(self, clip: ET.Element) -> None:
+        """Give every ``<tracking-shape>`` inside a just-deepcopy'd *clip* a
+        fresh document-unique id.
+
+        Same mechanism as ``_reassign_text_style_ids``: ``split_clip``/
+        ``cut_clip_ranges`` deepcopy the clip once per resulting segment, so
+        Cinematic object-tracking data (``<object-tracker><tracking-shape
+        id="tr1">``, preserved from the source asset's sidecar) keeps the
+        exact same id in every copy. A single cut is harmless — but the
+        batch chain re-cuts the same clip at each step, multiplying the
+        duplicate until the DTD validator rejects the file with "ID tr1
+        already defined".
+        """
+        for shape in clip.findall('.//tracking-shape'):
+            old_id = shape.get('id')
+            if not old_id:
+                continue
+            base = re.sub(r'_\d+$', '', old_id)
+            new_id = self._unique_tracking_shape_id(base)
+            if new_id == old_id:
+                continue
+            shape.set('id', new_id)
+
     def _make_text_title_clip(
         self,
         effect_id: str,