A library for manipulating C3D binary files

c3d, motion-capture
pip install c3d==0.5.1



This is a small library for reading and writing C3D binary files. C3D files are a standard format for recording 3-dimensional time sequence data, especially data recorded by a 3D motion tracking apparatus.


Install with pip:

pip install c3d

Or if you'd like to use the bleeding-edge version, just clone the github repository and build and install using the normal Python setup process:

pip install git+https://github.com/EmbodiedCognition/py-c3d



This package includes a script for converting C3D motion data to CSV format (c3d2csv) and an OpenGL-based visualization tool for observing the motion described by a C3D file (c3d-viewer).

Note for the viewer you need to install pyglet. This can be done by installing the gui extra of py-c3d:

pip install "c3d[gui]"


To use the C3D library, just import the package and create a Reader or Writer depending on your intended usage

import c3d

with open('data.c3d', 'rb') as handle:
    reader = c3d.Reader(handle)
    for i, (points, analog) in enumerate(reader.read_frames()):
        print('Frame {}: {}'.format(i, points.round(2)))

You can also get and set metadata fields using the library; see the package documentation for more details.

Developer Install

To work on c3d, first install poetry and then run:

git clone https://github.com/EmbodiedCognition/py-c3d
cd py-c3d
poetry install

This will create a new virtual environment with all the required dependency and c3d in develop mode.


To run tests available in the test folder, following command can be run from the root of the package directory:

python -m unittest discover .

Test scripts will automatically download test files from c3d.org.


This library is minimally effective, in the sense that the only motion tracking system I have access to (for testing) is a Phasespace system. If you try out the library and find that it doesn't work with your motion tracking system, let me know. Pull requests are also welcome!

Also, if you're looking for more functionality than just reading and writing C3D files, there are a lot of better toolkits out there that support a lot more file formats and provide more functionality, perhaps at the cost of increased complexity. The biomechanical toolkit is a good package for analyzing motion data.