From an image of a person in action, we can easily guess the 3D motion of the person in the immediate past and future. This is because we have a mental model of 3D human dynamics that we have acquired from observing visual sequences of humans in motion. We present a framework that can similarly learn a representation of 3D dynamics of humans from video via a simple but effective temporal encoding of image features. At test time, from video, the learned temporal representation can recover smooth 3D mesh predictions. From a single image, our model can recover the current 3D mesh as well as its 3D past and future motion. Our approach is designed so it can learn from videos with 2D pose annotations in a semi-supervised manner. However, annotated data is always limited. On the other hand, there are millions of videos uploaded daily on the Internet. In this work, we harvest this Internet-scale source of unlabeled data by training our model on them with pseudo-ground truth 2D pose obtained from an off-the-shelf 2D pose detector. Our experiments show that adding more videos with pseudo-ground truth 2D pose monotonically improves 3D prediction performance. We evaluate our model on the recent challenging dataset of 3D Poses in the Wild and obtain state-of-the-art performance on the 3D prediction task without any fine-tuning. The project website with video can be found at https://akanazawa.github.io/human_dynamics/.

通过观察人类运动的视觉序列，我们可以轻松猜测人在过去和未来的3D运动。我们提出了一个可以学习人类3D动力学表示的框架，通过简单而有效的图像特征时间编码。在测试过程中，学习到的时空表示能够预测具有平稳性的3D网格。我们的模型可以从单个图像中恢复当前的3D网格以及它未来和过去的3D运动，同时也可以通过半监督学习从带有2D姿态标注的自然视频中学习。我们通过对来自互联网海量未标记数据的模型训练，通过已有的2D姿态检测器得到伪基础真值2D姿态，证明了我们的模型可以自举学习并在三维动作预测任务中获得最新的性能。

从视频中学习三维人体动力学