Trace Anything: Representing Any Video in 4D via Trajectory Fields

Xinhang Liu^1,2     Yuxi Xiao^1,3     Donny Y. Chen¹     Jiashi Feng¹    
Yu-Wing Tai⁴     Chi-Keung Tang²     Bingyi Kang¹    

¹Bytedance Seed     ²HKUST     ³Zhejiang University     ⁴Dartmouth College

Overview

We propose a 4D video representation, trajectory field, which maps each pixel across frames to a continuous, parametric 3D trajectory. With a single forward pass, the Trace Anything model efficiently estimates such trajectory fields for any video, image pair, or unstructured image set. This repository provides the official PyTorch implementation for running inference with the Trace Anything model and exploring trajectory fields in an interactive 3D viewer.

Setup

Create and activate environment

# Clone the repository
git clone https://github.com/ByteDance-Seed/TraceAnything.git
cd TraceAnything

# Create and activate environment
conda create -n trace_anything python=3.10
conda activate trace_anything

Requirements

• Python ≥ 3.10

• PyTorch (install according to your CUDA/CPU setup)

• Dependencies:

  pip install einops omegaconf pillow opencv-python viser imageio matplotlib torchvision

Notes

• CUDA: Tested with CUDA 12.8.
• GPU Memory: The provided examples are tested to run on a single GPU with ≥ 48 GB VRAM.

Model weights

Download the pretrained model and place it at:

checkpoints/trace_anything.pt

Inference

We provide example input videos and image pairs under examples/input. Each subdirectory corresponds to a scene:

examples/
  input/
    scene_name_1/
      ...
    scene_name_2/
      ...

The inference script loads images from these scene folders and produces outputs.

---

Notes

• Images must satisfy W ≥ H. (Portrait images are automatically transposed.)
• Images are resized so that the long side = 512, then cropped to the nearest multiple of 16 (a model requirement).
• If the number of views exceeds 40, the script automatically downsamples.
• (Advanced) The script assumes input images are ordered in time (e.g., video frames or paired images). Support for unstructured, unordered inputs will be released in the future.

---

Running inference

Run the model over all scenes:

python scripts/infer.py

Default arguments

You can override these paths with flags:

• --config configs/eval.yaml
• --ckpt checkpoints/trace_anything.pt
• --input_dir examples/input
• --output_dir examples/output

Example

python scripts/infer.py \
  --input_dir examples/input \
  --output_dir examples/output \
  --ckpt checkpoints/trace_anything.pt

Results are saved to:

<output_dir>/<scene>/output.pt

---

What’s inside output.pt?

• preds[i]['ctrl_pts3d'] — 3D control points, shape [K, H, W, 3]

• preds[i]['ctrl_conf'] — confidence maps, shape [K, H, W]

• preds[i]['fg_mask'] — binary mask [H, W], computed via Otsu thresholding on control-point variance. (Mask images are also saved under <output_dir>/<scene>/masks.)

• preds[i]['time'] — predicted scalar time ∈ [0, 1).

  Even though the true timestamp is implicit from known sequence order, the network’s timestamp head still estimates it.

• views[i]['img'] — normalized input image tensor ∈ [-1, 1]

Optional: User-Guided Masks with SAM2

If you prefer user-guided SAM2 masks instead of the automatic masks computed from Trace Anything outputs (for visualization), we provide a helper script scripts/user_mask.py. This script lets you interactively select points on the first frame of a scene to produce per-frame foreground masks.

Install SAM2 and download its checkpoint. Then run with:

python scripts/user_mask.py --scene <output_scene_dir> \
  --sam2_cfg configs/sam2.1/sam2.1_hiera_l.yaml \
  --sam2_ckpt <path_to_sam2_ckpt>

This will saves masks to:

<scene>/masks/{i:03d}_user.png

It also updates <scene>/output.pt with:

preds[i]["fg_mask_user"]

When visualizing, fg_mask_user will automatically be preferred over fg_mask if available.

Interactive Visualization 🚀

Our visualizer lets you explore the trajectory field interactively:

Fire up the interactive 3D viewer and dive your trajectory fields:

python scripts/view.py --output examples/output/<scene>/output.pt

Useful flags

• --port 8020 — set viewer port
• --t_step 0.025 — timeline step (smaller = more fine-grained curve evaluation)
• --ds 2 — downsample all data by ::2 for extra speed

Remote use (SSH port-forwarding)

ssh -N -L 8020:localhost:8020 <user>@<server>
# Then open http://localhost:8020 locally

Trajectory panel

Input a frame number, or simply type "mid" / "last". Then hit Build / Refresh to construct trajectories, and toggle Show trajectories to view them.

Play around! 🎉

• Pump up or shrink point size
• Filter out noisy background / foreground points by confidence
• Drag to swivel the viewpoint
• Slide through time and watch the trajectories evolve

Acknowledgements

We sincerely thank the authors of the open-source repositories DUSt3R, Fast3R, VGGT, MonST3R, Easi3R, St4RTrack, POMATO, SpaTrackerV2 and Viser for their inspiring and high-quality work that greatly contributed to this project.

License

• Code: Licensed under the Apache 2.0 License.
• Model weights: Licensed under the CC BY-NC 4.0 License. These weights are provided for research and non-commercial use only.

Citation

If you find our repository useful, please consider giving it a star ⭐ and citing our paper in your work:

@misc{liu2025traceanythingrepresentingvideo,
      title={Trace Anything: Representing Any Video in 4D via Trajectory Fields}, 
      author={Xinhang Liu and Yuxi Xiao and Donny Y. Chen and Jiashi Feng and Yu-Wing Tai and Chi-Keung Tang and Bingyi Kang},
      year={2025},
      eprint={2510.13802},
      archivePrefix={arXiv},
      primaryClass={cs.CV},
      url={https://arxiv.org/abs/2510.13802}, 
}