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MARS : A Machine Learning Model for Identifying Actions from Videos

This is an introduction to「MARS」, a machine learning model that can be used with ailia SDK. You can easily use this model to create AI applications using ailia SDK as well as many other ready-to-use ailia MODELS.


MARS (Motion-Augmented RGB Stream for Action Recognition) is a model proposed in May 2019, which detects actions taking place in an input video.

MARS has been trained using HMDB51 and is capable of recognizing the following 51 actions.


Features of MARS

There are two types of detecting actions from video: one is skeleton-based, which uses LSTM or CNN after detecting the skeleton with OpenPose, and the other is 3D Convolution, which uses RGB and optical flow of the video. MARS is a direct detection architecture.

There are also two types of action detection methods directly from video: two-stream CNNs, which use a single frame of RGB and multiple optical flows, and 3-D XYT CNNs, which use multiple frames of RGB and multiple optical flows.


MARS is an improvement of 3-D XYT CNNs.

3-D XYT CNNs detect actions by providing both multiple RGB images and a Flow stream consisting of motion vectors for each pixel. The problem is that the computation of the motion vectors for each pixel is very demanding.

MARS uses Flow stream during training, but only RGB images during inference. This makes it possible to detect actions much faster.


Using MARS, actions can be recognized at high speed and with high accuracy. For example, it is 100 times faster and more accurate than RGB+TVL1Flow, which uses Flow along with RGB. Running on a TitanX, it takes 30 seconds to calculate TVL1 Flow for one video. Since 99% of the cost of action detection is spent to compute optical flow, MARS can infer 100 times faster since it does not need this computation.


MARS takes 16 frames of images as input and uses 3D CNN for inference. resnet50, resnet101 and resnet152 are used as backbone.


3D convolutions required to run Mars are supported since ailia SDK 1.2.4.

Use the following command to detect the action of any video.

$ python3 -v input_video.mp4

ax Inc. has developed ailia SDK, which enables cross-platform, GPU-based rapid inference.

ax Inc. provides a wide range of services from consulting and model creation, to the development of AI-based applications and SDKs. Feel free to contact us for any inquiry.



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