Notes for Paper “Unsupervised Learning of Video Representations using LSTMs”

Paper: Srivastava, Nitish, Elman Mansimov, and Ruslan Salakhudinov. “Unsupervised learning of video representations using lstms.” International conference on machine learning. 2015.

  • Basics
    • Gradient vanishing problem.
      • Solution: LSTM (Long short term Memory)
    • Unsupervised learning model
      • Crucial to have the right inductive biases and right objective functions.
  • Main methods
    • LSTM encoder to get representations of videos
    • Multi-LSTM decoders for different tasks.  — Produce a target sequence
      • Different choices of target sequences.
        • Same as input
        • To predict the future
    • Inputs: — two kinds
      • Image patches
      • High level percepts
    • Simple squared loss function as a starting point
    • Encoder-decoder RNN that can be used with any loss functions.
    • LSTM details
      • Cell: memory unit
      • Input date, forget date and output date
    • LSTM autoencoder model
      • Two RNNs: encoder and decoder
      • Input: a sequence of vectors
      • After the last input been read, the decoder start to do prediction and output the sequence
      • Output: Same as input sequence, reverse order
    • LSTM future predictor model
      • Predict only the next frame at each time step
    • Combination of the above two models
  • Take home messages
  • Other methods mentioned — for video representations learning
    • Supervised learning: 3D convolutional nets.
    • Unsupervised learning:
      • ICA (Independence subspace analysis)
      • Generative models for understanding transformations between 2 consecutive images
      • Generative model for predicting next frame or interpolate between frames — Important to choose right loss function — Not square loss function

 

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