title: How to get SubType Guid for MediaExtensionManager.RegisterAudioDecoder(...)?
body: <p>I'm trying to write a custom decoder for a windows store app (using Media Foundation like in this <a href="https://code.msdn.microsoft.com/windowsapps/Media-extensions-sample-7b466096/view/SourceCode" rel="nofollow">sample</a>).
  I'm at the point where I want to try to register the decoder.</p>
  
  <p>As you can see <a href="http://msdn.microsoft.com/en-US/library/windows/apps/br240991" rel="nofollow">here</a> the method to register an audio decoder looks like this:</p>
  
  <pre><code>public void RegisterAudioDecoder(
    string activatableClassId, 
    Guid inputSubtype, 
    Guid outputSubtype
  )
  </code></pre>
  
  <p>However I do not know what I should enter as the input subtype Guid?</p>
  
  <p>Where do I get the required Guid?</p>
  
  <p>There are some subtype Guids predefined but they are obviously only for the formats that are already supported.
  Is there any way I can get the Guid from a file of the codec I want to decode?</p>