title: Programmatically change the speed of an audio file in real-time
body: <h2>Environment</h2>
  
  <ul>
  <li>Hardware: Raspberry Pi x</li>
  <li>O.S.: Raspbian Jessie Lite</li>
  <li>Language: Qt5 / C++</li>
  </ul>
  
  <h2>Goal</h2>
  
  <p>Execute an audio file (wav or better mp3) changing its speed smoothly and countinuosly. The pitch should change according to the speed (playback rate).
  My application updates several times per second a variable that contains the desired speed: i.e. 1.0 = normal speed. Required range is about 0.2 .. 3.0, with a resolution of 0.01.</p>
  
  <p>The audio is likely music, expected format: mono, 16-bit, 11.025 Hz.
  No specific constraints about latency: below 500 ms is acceptable.</p>
  
  <h2>Some thougths</h2>
  
  <p>QMediaPlayer in QtMultimedia has the playbackRate property that should do exactly this. Unfortunately I have never be able to make QtMultimedia work in my systems.</p>
  
  <p>It's ok to use also an external player, and send data using pipes or any IPC.</p>
  
  <p>How would you achieve this?</p>