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README.md

@@ -534,7 +534,28 @@ Each scene includes a `caption.txt` file containing an English paragraph that de
 <h3 id="trajectories" style="font-size: 1.35em; margin-top: 0.75em; margin-bottom: 0.22em; line-height: 1.2; margin-left: 0;"><span style="display: inline-block; width: 1.08em;">•</span>Trajectories</h3>
 <div style="margin-left: 16px;">
 
-TODO
+Each sequence includes a JSON file with the same name as the sequence. This file records the per-frame poses of selected dynamic objects, including their rotations and translations in the world coordinate system.
+
+The JSON file contains two main parts:
+
+- `sequence_info`: basic information about the sequence, such as the total number of frames and the frame rate (`fps`).
+- `actors`: pose and metadata for dynamic objects, including object category, asset index path, actor type, and transformation data.
+
+For each actor, the storage format depends on its `actor_type`:
+
+- If `actor_type` is `solid`, the object is treated as a single rigid body. Its per-frame pose is stored in the actor-level `transform_data` field, while the `components` field is empty.
+- If `actor_type` is `interactable`, the object is represented by multiple components. The actor-level `transform_data` field is empty, and the per-component poses are stored under `components[component_name].transform_data`.
+
+Each entry in `transform_data` describes the pose of the object or component at a specific frame:
+
+- `frame`: frame index in the sequence
+- `time_seconds`: timestamp of the frame in seconds
+- `transform`: object or component transformation, including:
+  - `location`: 3D position
+  - `rotation`: rotation quaternion
+  - `scale`: 3D scale
+
+</div>
 
 </div>