title: Keras: Embedding layer + LSTM: Time Dimension
body: <p>This might be too stupid to ask ... but ...</p>
  
  <p>When using LSTM after the initial <code>Embedding</code> layer in Keras (for example the <a href="https://github.com/fchollet/keras/blob/master/examples/imdb_lstm.py" rel="nofollow noreferrer">Keras LSTM-IMDB tutorial code</a>), how does the <code>Embedding</code> layer know that there is a time dimension? In another word, how does the <code>Embedding layer know</code>the length of each sequence in the training data set? How does the Embedding layer know I am training on sentences, not on individual words? Does it simply infer during the training process?</p>