I-JEPA

Revisiting Feature Prediction for Learning Visual Representations from Video (V-JEPA)

No use of pre-training. Why don’t you believe in the power of pre-training? This is more to show that we need better architecture for better representation learning than auto-regressive models.

Pre-trained on 2 million videos (referred as VideoMix2M), which combines:

• HowTo100M (HT) (Miech et al.,2019),
• Kinetics-400/600/700 (K710) (Kay et al., 2017),
• Something-Something-v2 (SSv2) (Goyal et al., 2017), removes overlap with validation set of Kinetics-400/600/700 and Something-Something-v2.

Loss Objective

They talk about mode collapse if we just use the naive regression objective $minimiz{e}_{\theta ,\varphi }\Vert P_{\varphi }(E_{\theta }(x),{\Delta }_y)-E_{\theta }(y){\Vert }_1$

• $E_{\theta }$ is the encoder network
• $P_{\varphi }$ is the predictor network

So they use a stop-gradient operation: $minimiz{e}_{\theta ,\varphi }\Vert P_{\varphi }(E_{\theta }(x),{\Delta }_y)-sg({\overline{E}}_{\theta }(y)){\Vert }_1$

• ${\overline{E}}_{\theta }(y)$ is an EMA of the x-encoder’s weights
• $\Delta y$ is a learnable mask token that indicates the locations of the dropped patches

Video benchmarks

• VideoGLUE
• K400
• SSv2
• AVA

Image benchmarks

• ImageNet