Variable Sequence Lengths in TensorFlow

I recently wrote a guide on recurrent networks in TensorFlow. That covered the basics but often we want to learn on sequences of variable lengths, possibly even within the same batch of training examples. In this post, I will explain how to use variable length sequences in TensorFlow and what implications they have on your model. Since TensorFlow unfolds our recurrent network for a given number of steps, we can only feed sequences of that shape to the network. We also want the input to have a fixed size so that we can represent a training batch as a single tensor of shape batch_size x max_length x frame_size.