Creates dataset from in-memory predictions.

def get_zipped_dataset_from_predictions(predictions):
  """Creates dataset from in-memory predictions."""
  targets = stack_data_given_key(predictions, "targets")
  outputs = stack_data_given_key(predictions, "outputs")
  num_videos, num_steps = targets.shape[:2]

  # Truncate output time-steps to match target time-steps
  outputs = outputs[:, :num_steps]

  targets_placeholder = tf.placeholder(targets.dtype, targets.shape)
  outputs_placeholder = tf.placeholder(outputs.dtype, outputs.shape)
  dataset = tf.data.Dataset.from_tensor_slices(
      (targets_placeholder, outputs_placeholder))
  iterator = dataset.make_initializable_iterator()
  feed_dict = {targets_placeholder: targets,
               outputs_placeholder: outputs}
  return iterator, feed_dict, num_videos