| --- |
| license: cc-by-4.0 |
| pretty_name: "Syn4D windows with ground-truth Track4D caches (Track4DGEN v3)" |
| viewer: false |
| tags: |
| - 4d |
| - video |
| - synthetic |
| - point-tracking |
| - depth |
| - 3d-bounding-boxes |
| size_categories: |
| - 1K<n<10K |
| --- |
| |
| # Syn4D windows with ground-truth Track4D caches (Track4DGEN v3) |
|
|
| 5,817 windows cut from **[Syn4D](https://huggingface.co/datasets/Syn4D/Syn4D)** (V1, revision |
| [`bb08d13f`](https://huggingface.co/datasets/Syn4D/Syn4D/tree/bb08d13faabc0649a4a938030025e9e2b32a6189)), each with an |
| annotation cache in Track4D's cache format: instance masks, metric depth, cameras, point trajectories and 3D boxes |
| built from Syn4D's own ground truth, no learned model involved. They are the input of the GPU stage of Track4DGEN's |
| v3 pair preprocessing (memory / control condition export, target latents, caption embeddings) for SanaTrack training. |
|
|
| This is a derivative of Syn4D, not an official Syn4D release. Please cite Syn4D |
| ([arXiv:2605.05207](https://arxiv.org/abs/2605.05207), [project page](https://jzr99.github.io/Syn4D/)) when you use it. |
|
|
| ## Contents |
|
|
| | | | |
| |---|---| |
| | Scenes | 29 (Syn4D V1) | |
| | Windows | 5,817 — 129 / 97 / 65 frames: 2,292 / 2,022 / 1,503 — at 15 fps (every 2nd frame of the 30 fps renders) | |
| | Default pairs | 12,423 memory → target chunk pairs of 33 frames (gap 0 / 32 / 64 frames: 5,817 / 4,314 / 2,292) | |
| | Kept by the instance selection | 12,048 pairs (97.0 %), 35,779 of 41,594 instance-pairs (`dynamic_first_v3` with boxes standing on the ground-truth gravity) | |
| | Captions | every window: Syn4D's captions for 3 scenes, Qwen3-VL-8B-Instruct for the 26 scenes that ship none | |
| | Size | 108.5 GB (101 GiB) in 29 uncompressed tar shards, one per scene (1.0–7.0 GB) | |
|
|
| Left out: hallway's sequences without tracking records in the source (7 windows), sequences shorter than 65 |
| frames at 15 fps, and the `syn4d_sim` subset. |
|
|
| ## Layout |
|
|
| ```text |
| README.md |
| index_b.jsonl one row per window (paths relative to the dataset root) |
| shards/syn4d_tracks-<scene>.tar syn4d_tracks/<scene>/<window>/{clip.mp4, track/...} |
| SHA256SUMS every file of this repository |
| LICENSE LICENSES/ THIRD_PARTY_NOTICES.md sequence_to_asset_mapping.csv Syn4D's, unchanged |
| ``` |
|
|
| Download and extract every shard into one folder; the index's paths are relative to it: |
|
|
| ```bash |
| hf download HugMinjun/Syn4D-Track4D-v3 --repo-type dataset --local-dir Syn4D-Track4D-v3 |
| cd Syn4D-Track4D-v3 && sha256sum -c SHA256SUMS && for t in shards/*.tar; do tar -xf "$t"; done |
| ``` |
|
|
| Track4DGEN's `tools/syn4d/hf_download.py` does the same scene by scene (checksums, extraction, deleting each tar). |
|
|
| ### Index rows (`index_b.jsonl`) |
| |
| ```json |
| {"path": "syn4d_tracks/arena/seq_000000_0_w0_n129/clip.mp4", "id": "syn4d:arena:seq_000000_0:w0:n129", |
| "source_id": "syn4d:arena:seq_000000_0:w0:n129", "caption": "Three individuals are on a wooden platform ...", |
| "split": "train", "frames": 129, "tracking_frames": 129, "fps": 15.0, |
| "tracks": "syn4d_tracks/arena/seq_000000_0_w0_n129/track", "metric_reference": {"scale": 1.0}, |
| "gravity_up_world": [0.002167, -0.680545, -0.732703]} |
| ``` |
| |
| - `id`: `syn4d:<scene>:<sequence>:w<window>:n<frames>`; `<scene>` / `<sequence>` are Syn4D's names. |
| - `gravity_up_world`: the world's up (Unreal's +Z) in the window's coordinate frame, a unit vector, from Syn4D's camera |
| CSVs. |
| - `metric_reference: {"scale": 1.0}`: the caches are already in metres. |
| |
| ### Window folder (`syn4d_tracks/<scene>/<window>/`) |
| |
| - `clip.mp4`: the window's renders, H.264, 1280 × 720, 15 fps (training crops the centre 704 × 1280). |
| - `track/compact.npz` (T frames, N tracked instances, Q query points): |
| |
| | Array | Shape, type | Meaning | |
| |---|---|---| |
| | `cam_R`, `cam_t` | (T, 3, 3), (T, 3) float32 | camera-to-world; world = the window's first camera, OpenCV axes, metres | |
| | `intrinsics` | (T, 3, 3) float32 | at the 308 × 560 tracker resolution (of the 704 × 1280 crop) | |
| | `depth16` | (T, 308, 560) float16 | z-depth in metres, NaN where invalid | |
| | `all_masks`, `query_masks` | (T, 704, 1280), (704, 1280) uint8 | 0 background, 1..N tracked moving instances, 200 moving pixels that are not tracked (objects appearing later, pixels that are neither environment nor an object) | |
| | `fg_prob` | (T, 308, 560) uint8 | foreground probability | |
| | `traj`, `conf`, `vis_logits` | (T, Q, 3), (T, Q), (T, Q) float32 | world trajectories of the query points, their confidence and visibility | |
| | `query_xyz`, `query_uv`, `query_instance` | (Q, 3), (Q, 2), (Q,) | the queries in the first frame and their instance | |
| | `pose`, `T_world_from_canon`, `corners`, `half`, `scale`, `pose_valid` | (N, T, ...) | per-frame 3D boxes of the tracked instances | |
| | `box0_center`, `box0_R`, `box0_half`, `instance_ids` | (N, ...) | first-frame boxes, instance ids | |
| |
| - `track/box_refit.{npz,json}`: per-frame boxes re-fitted from the masks and the depth (median size); Track4DGEN's |
| cache loader applies them over `compact.npz`'s boxes. |
| - `track/result.json`: per-instance metadata and the Syn4D source (`syn4d`: scene, sequence, frame range, groups); |
| `track/observations.json`, `track/sampling.json`: Track4DGEN's observation and sampling metadata. |
| |
| ## How it was made |
| |
| From Syn4D V1 (stride-1 bundle: frames, depth, masks, cameras and tracking records; stride-5 bundle: the window |
| index, captions and the camera CSVs for the gravity), on CPUs only (Track4DGEN `tools/syn4d`, branch `datasets/syn4d`): |
| |
| 1. Windows of 129 / 97 / 65 frames at 15 fps over each sequence. |
| 2. Cameras: Syn4D's CSV rows (Unreal centimetres, left-handed) to OpenCV camera-to-world in metres, relative to the |
| window's first camera. Depth: EXR depth ÷ 100. |
| 3. Instances: one per Syn4D mesh group (a person's body and clothing are one instance). Since every Syn4D object is |
| animated, an object counts as static only if the 90th percentile of its faces' displacement stays under 1 cm; |
| moving objects visible in the first frame are tracked, the others get id 200. |
| 4. Trajectories: each query's first-frame mesh face is found again in every frame through Syn4D's tracking records. |
| 5. Boxes: Track4D's fitting code, then re-fitted per frame from masks and depth. |
| 6. Captions: the sequence's Syn4D caption where the scene ships them, otherwise Qwen3-VL-8B-Instruct (`0c351dd`) over |
| 8 frames of the sequence. |
| |
| The renders, depth, masks, cameras and tracking records are Syn4D's; this dataset changes their frame rate, crops, |
| units and coordinate frames, and adds the caches and the generated captions. |
| |
| ## License and third-party assets |
| |
| Released under **CC BY 4.0**, like Syn4D. Syn4D's `LICENSE`, `LICENSES/`, `THIRD_PARTY_NOTICES.md` and |
| `sequence_to_asset_mapping.csv` are included unchanged and apply to this dataset as they do to Syn4D: |
| |
| - **BEDLAM2**: every sequence of these 29 scenes depends on BEDLAM2 bodies (`asset_type` `bedlam2_body` in the mapping). |
| As for Syn4D, no BEDLAM2 data is redistributed here, and you must obtain BEDLAM2 from its official source and agree |
| to the BEDLAM2 license before using BEDLAM2-dependent sequences. |
| - Fab / Unreal scenes (Fab Standard License), Objaverse objects (ODC-By 1.0, each object under its own license), |
| Google Scanned Objects (CC BY 4.0): see `THIRD_PARTY_NOTICES.md`. No rights to third-party assets are granted. |
| |
