Extracting dense flow field given a video.

Depencies:

• LibZip: to install on ubuntu apt-get install libzip-dev on mac brew install libzip

For OpenCV 3 Users

Please see the opencv-3.1 branch. Many thanks to @victorhcm for the contributions!

Install

git clone --recursive http://github.com/yjxiong/dense_flow

Build

mkdir build && cd build
# `export OpenCV_DIR=/path/to/opencv-2.4.13/release/` if necessary
cmake -D CUDA_USE_STATIC_CUDA_RUNTIME=OFF .. 
make -j

Build problems and solutions

1. Error: cannot find -lopencv_dep_cudart
   solution: add -D CUDA_USE_STATIC_CUDA_RUNTIME=OFF when build dense_flow

   cmake -D CUDA_USE_STATIC_CUDA_RUNTIME=OFF ..

2. Can't find right OpenCV version and path
   Export opencv build path(containing the OpenCVConfig.cmake file) before make ..

   export OpenCV_DIR=/path/to/opencv-2.4.13/release/

   reference

3. Boost python version problem
   ImportError: /dense_flow/build/libpydenseflow.so: undefined symbol: _ZN5boost6python6detail11init_moduleER11PyModuleDefPFvvE
   Solution: Modify line 23 of CMakeLists.txt to FIND_PACKAGE(PythonLibs 2.7 REQUIRED). The default one is for Python3.5m

Usage

./extract_gpu -f test.avi -x tmp/flow_x -y tmp/flow_y -i tmp/image -b 20 -t 1 -d 0 -s 1 -o dir

• test.avi: input video
• tmp: folder containing RGB images and optical flow images
• dir: output generated images to folder. if set to zip, will write images to zip files instead.

Warp Flow

The warp optical flow is used in the following paper

@inproceedings{TSN2016ECCV,
  author    = {Limin Wang and
               Yuanjun Xiong and
               Zhe Wang and
               Yu Qiao and
               Dahua Lin and
               Xiaoou Tang and
               Luc {Van Gool}},
  title     = {Temporal Segment Networks: Towards Good Practices for Deep Action Recognition},
  booktitle   = {ECCV},
  year      = {2016},
}

To extract warp flow, use the command

./extract_warp_gpu -f test.avi -x tmp/flow_x -y tmp/flow_y -i tmp/image -b 20 -t 1 -d 0 -s 1 -o dir