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PWC-Net: CNNs for Optical Flow Using Pyramid, Warping, and Cost Volume frames are extracted for every consecutive pair of frames in a video. PWC-Net is pre-trained on Sintel Flow dataset. The implementation follows sniklaus/pytorch-pwc@f61389005.

CUDA 11 and GPUs like RTX 3090 and newer

The current environment does not support CUDA 11 and, therefore, GPUs like RTX 3090 and newer. For details please check this issue #13 If you were able to fix it, please share your workaround. If you need an optical flow extractor, you are recommended to use RAFT.

The PWC-Net does NOT support using CPU currently

The PWC-Net uses cupy module, which makes it difficult to turn to a version that does not use the GPU. However, if you have solution, you may submit a PR.

Set up the Environment for PWC

Setup conda environment.

# it will create a new conda environment called 'pwc' on your machine
conda env create -f conda_env_pwc.yml

Quick Start

Activate the environment

conda activate pwc

and extract optical flow from ./sample/v_GGSY1Qvo990.mp4 and show the flow for each frame

python \
    feature_type=pwc \
    device="cuda:0" \
    show_pred=true \

Note, if show_pred=true, the window with predictions will appear, use any key to show the next frame. To use show_pred=true, a screen must be attached to the machine or X11 forwarding is enabled.

Supported Arguments

batch_size 1 You may speed up extraction of features by increasing the batch size as much as your GPU permits.
extraction_fps null If specified (e.g. as 5), the video will be re-encoded to the extraction_fps fps. Leave unspecified or null to skip re-encoding.
side_size null If resized to the smaller edge (resize_to_smaller_edge=true), then min(W, H) = side_size, if to the larger: max(W, H), if null (None) no resize is performed.
resize_to_smaller_edge true If false, the larger edge will be used to be resized to side_size.
device "cuda:0" The device specification. It follows the PyTorch style. Use "cuda:3" for the 4th GPU on the machine or "cpu" for CPU-only.
video_paths null A list of videos for feature extraction. E.g. "[./sample/v_ZNVhz7ctTq0.mp4, ./sample/v_GGSY1Qvo990.mp4]" or just one path "./sample/v_GGSY1Qvo990.mp4".
file_with_video_paths null A path to a text file with video paths (one path per line). Hint: given a folder ./dataset with .mp4 files one could use: find ./dataset -name "*mp4" > ./video_paths.txt.
on_extraction print If print, the features are printed to the terminal. If save_numpy or save_pickle, the features are saved to either .npy file or .pkl.
output_path "./output" A path to a folder for storing the extracted features (if on_extraction is either save_numpy or save_pickle).
keep_tmp_files false If true, the reencoded videos will be kept in tmp_path.
tmp_path "./tmp" A path to a folder for storing temporal files (e.g. reencoded videos).
show_pred false If true, the script will visualize the optical flow for each pair of RGB frames.


Please see the examples for RAFT optical flow frame extraction. Make sure to replace --feature_type argument to pwc.


  1. The PWC-Net paper and official implementation.
  2. The PyTorch implementation used in this repo.


The wrapping code is under MIT, but PWC Net has GPL-3.0