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Last Commit
Mar. 26, 2019
Aug. 2, 2017

I3D models trained on Kinetics


This repository contains trained models reported in the paper "Quo Vadis, Action Recognition? A New Model and the Kinetics Dataset" by Joao Carreira and Andrew Zisserman. The paper was posted on arXiv in May 2017, and will be published as a CVPR 2017 conference paper.

"Quo Vadis" introduced a new architecture for video classification, the Inflated 3D Convnet or I3D. Here we release Inception-v1 I3D models trained on the Kinetics dataset training split.

In our paper, we reported state-of-the-art results on the UCF101 and HMDB51 datasets from fine-tuning these models. I3D models pre-trained on Kinetics also placed first in the CVPR 2017 Charades challenge.

NEW: added a new pre-trained checkpoint using rgb inputs and trained from scratch on Kinetics-600.

Disclaimer: This is not an official Google product.

Running the code


First follow the instructions for installing Sonnet.

Then, clone this repository using

$ git clone

Sample code

Run the example code using

$ python

With default flags, this builds the I3D two-stream model, loads pre-trained I3D checkpoints into the TensorFlow session, and then passes an example video through the model. The example video has been preprocessed, with RGB and Flow NumPy arrays provided (see more details below).

The script outputs the norm of the logits tensor, as well as the top 20 Kinetics classes predicted by the model with their probability and logit values. Using the default flags, the output should resemble the following up to differences in numerical precision:

Norm of logits: 138.468643

Top classes and probabilities
1.0 41.8137 playing cricket
1.49716e-09 21.494 hurling (sport)
3.84312e-10 20.1341 catching or throwing baseball
1.54923e-10 19.2256 catching or throwing softball
1.13602e-10 18.9154 hitting baseball
8.80112e-11 18.6601 playing tennis
2.44157e-11 17.3779 playing kickball
1.15319e-11 16.6278 playing squash or racquetball
6.13194e-12 15.9962 shooting goal (soccer)
4.39177e-12 15.6624 hammer throw
2.21341e-12 14.9772 golf putting
1.63072e-12 14.6717 throwing discus
1.54564e-12 14.6181 javelin throw
7.66915e-13 13.9173 pumping fist
5.19298e-13 13.5274 shot put
4.26817e-13 13.3313 celebrating
2.72057e-13 12.8809 applauding
1.8357e-13 12.4875 throwing ball
1.61348e-13 12.3585 dodgeball
1.13884e-13 12.0101 tap dancing

Running the test

The test file can be run using

$ python

This checks that the model can be built correctly and produces correct shapes.

Further details

Provided checkpoints

The default model has been pre-trained on ImageNet and then Kinetics; other flags allow for loading a model pre-trained only on Kinetics and for selecting only the RGB or Flow stream. The script shows how to run all these combinations, generating the sample output in the out/ directory.

The directory data/checkpoints contains the four checkpoints that were trained. The ones just trained on Kinetics are initialized using the default Sonnet / TensorFlow initializers, while the ones pre-trained on ImageNet are initialized by bootstrapping the filters from a 2D Inception-v1 model into 3D, as described in the paper. Importantly, the RGB and Flow streams are trained separately, each with a softmax classification loss. During test time, we combine the two streams by adding the logits with equal weighting, as shown in the code.

We train using synchronous SGD using tf.train.SyncReplicasOptimizer. For each of the RGB and Flow streams, we aggregate across 64 replicas with 4 backup replicas. During training, we use 0.5 dropout and apply BatchNorm, with a minibatch size of 6. The optimizer used is SGD with a momentum value of 0.9, and we use 1e-7 weight decay. The RGB and Flow models are trained for 115k and 155k steps respectively, with the following learning rate schedules.


  • 0 - 97k: 1e-1
  • 97k - 108k: 1e-2
  • 108k - 115k: 1e-3


  • 0 - 97k: 1e-1
  • 97k - 104.5k: 1e-2
  • 104.5k - 115k: 1e-3
  • 115k - 140k: 1e-1
  • 140k - 150k: 1e-2
  • 150k - 155k: 1e-3

This is because the Flow models were determined to require more training after an initial run of 115k steps.

The models are trained using the training split of Kinetics. On the Kinetics test set, we obtain the following top-1 / top-5 accuracy:

Model ImageNet + Kinetics Kinetics
RGB-I3D 71.1 / 89.3 68.4 / 88.0
Flow-I3D 63.4 / 84.9 61.5 / 83.4
Two-Stream I3D 74.2 / 91.3 71.6 / 90.0

Sample data and preprocessing

The release of the DeepMind Kinetics dataset only included the YouTube IDs and the start and end times of the clips. For the sample data here, we use a video from the UCF101 dataset, for which all the videos are provided in full. The video used is v_CricketShot_g04_c01.mp4 which can be downloaded from the UCF101 website.

Our preprocessing uses internal libraries, but can be reproduced as follows. For both streams, we sample frames at 25 frames per second. For Kinetics, we additionally clip the videos at the start and end times provided.

For RGB, the videos are resized preserving aspect ratio so that the smallest dimension is 256 pixels, with bilinear interpolation. Pixel values are then rescaled between -1 and 1. During training, we randomly select a 224x224 image crop, while during test, we select the center 224x224 image crop from the video. The provided .npy file thus has shape (1, num_frames, 224, 224, 3) for RGB, corresponding to a batch size of 1.

For the Flow stream, after sampling the videos at 25 frames per second, we convert the videos to grayscale. We apply a TV-L1 optical flow algorithm, similar to this code from OpenCV. Pixel values are truncated to the range [-20, 20], then rescaled between -1 and 1. We only use the first two output dimensions, and apply the same cropping as for RGB. The provided .npy file thus has shape (1, num_frames, 224, 224, 2) for Flow, corresponding to a batch size of 1.

Here are gifs showing the provided .npy files. From the RGB data, we added 1 and then divided by 2 to rescale between 0 and 1. For the Flow data, we added a third channel of all 0, then added 0.5 to the entire array, so that results are also between 0 and 1.

See data/v_CricketShot_g04_c01_rgb.gif

See data/v_CricketShot_g04_c01_flow.gif

For additional details on preprocessing, please refer to our paper or contact the authors.


Brian Zhang, Joao Carreira, Viorica Patraucean, Diego de Las Casas, Chloe Hillier, and Andrew Zisserman helped to prepare this initial release. We would also like to thank the teams behind the Kinetics dataset and the original Inception paper on which this architecture and code is based.

Questions and contributions

To contribute to this repository, you will first need to sign the Google Contributor License Agreement (CLA), provided in the file. We will then be able to accept any pull requests, though are not currently aiming to expand to other trained models.

For any questions, you can contact the authors of the "Quo Vadis" paper, whose emails are listed in the paper.