convex optimization Action Detection Temporal Localization CVPR CS231n video 인공지능 연구 Video Representation Learning Self Supervised 2019 ICCV BMN Submodular Function Key-frame Selection Video-Summarization self-supervised learning Temporal Action Proposal AI 대학원 linear classifier representation learning AI대학원 loss function ICCV Gradient Descent DeepLearning Deep Learning optimization bsp 인턴 연구 KNN