code: def l1_error(true, pred):
      """L1 distance between tensors true and pred."""
      return tf.reduce_sum(tf.abs(true - pred)) / tf.to_float(
          tf.size(pred)
      )
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from six.moves import reduce
  from tensor2tensor.layers import common_layers
  from tensor2tensor.layers import common_video
  from tensor2tensor.models.video import epva_params
  from tensor2tensor.models.video import sv2p
  from tensor2tensor.utils import contrib
  from tensor2tensor.utils import registry
  import tensorflow.compat.v1
  from tensorflow.contrib.framework.python.ops import arg_scope
  from tensorflow.contrib.slim.python.slim.nets import vgg
label_desc: Use image node_id 11 for calling a global function with example usage: l1_error(true, pred) and returns: unknown