title: TFRecords: Write list of tensors to single Example
body: <p>I'm extracting features from images using a convolutional neural network. The network in question has three outputs (three output tensors), which differ in size. I want to store the extracted features in TFRecords, one Example for each image:</p>
  
  <pre><code>Example:
      image_id: 1
      features/fc8: [output1.1, output1.2, output1.3]
  Example:
      image_id: 2
      features/fc8: [output2.1, output2.2, output2.3]
  ....
  </code></pre>
  
  <p>How can I achieve this structure using TFRecords?</p>