  This work proposes a weakly-supervised temporal action localization
framework, called D2-Net, which strives to temporally localize actions using
video-level supervision. Our main contribution is the introduction of a novel
loss formulation, which jointly enhances the discriminability of latent
embeddings and robustness of the output temporal class activations with respect
to foreground-background noise caused by weak supervision. The proposed
formulation comprises a discriminative and a denoising loss term for enhancing
temporal action localization. The discriminative term incorporates a
classification loss and utilizes a top-down attention mechanism to enhance the
separability of latent foreground-background embeddings. The denoising loss
term explicitly addresses the foreground-background noise in class activations
by simultaneously maximizing intra-video and inter-video mutual information
using a bottom-up attention mechanism. As a result, activations in the
foreground regions are emphasized whereas those in the background regions are
suppressed, thereby leading to more robust predictions. Comprehensive
experiments are performed on multiple benchmarks, including THUMOS14 and
ActivityNet1.2. Our D2-Net performs favorably in comparison to the existing
methods on all datasets, achieving gains as high as 2.3% in terms of mAP at
IoU=0.5 on THUMOS14. Source code is available at
https://github.com/naraysa/D2-Net
