title: What audio formats are supported by Azure Cognitive Services' Speech Service (SST)?
body: <p>Bearing in mind that the Microsoft/Azure Cognitive Services' "Speech Service" is currently going through a rationalisation exercise, as far as I can tell from looking at</p>
  
  <p><a href="https://docs.microsoft.com/en-us/azure/cognitive-services/speech-service/rest-apis#speech-to-text" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/cognitive-services/speech-service/rest-apis#speech-to-text</a></p>
  
  <p><a href="https://docs.microsoft.com/en-us/azure/cognitive-services/speech/home" rel="nofollow noreferrer">https://docs.microsoft.com/en-us/azure/cognitive-services/speech/home</a></p>
  
  <p>only <code>.wav</code> binaries are acceptable, with anything else giving the response:</p>
  
  <pre><code>{"Message":"Unsupported audio format"}
  </code></pre>
  
  <p>Is there any other way to discover the acceptable audio formats/encodings/etc., or is this it?</p>
  
  <p>[Bonus points for tips on preprocessing arbitrary/<code>.m4a</code> audio formats in python <code>pydub</code> so that they meet the bar - currently works for <code>.mp3</code> but not for <code>.m4a</code>].</p>
  
  <p>Thanks!</p>