title: Modify audio output stream of QMediaPlayer
body: <p>I'm trying to port an audio player from Qt4 to Qt5, and from Phonon to QtMultimedia.
  Everything works fine with a QMediaPlayer, except that I can't find any way to modify the audio stream between the output of QMediaPlayer and the system sound.
  I would like to apply a post-processing effect to the audio. </p>
  
  <p>Any way to do this? Maybe by sub-classing QMediaPlayer? I've checked the QAudioOutput and QAudioDecoder classes but I would have to implement a lot of things to get the same behaviour as QMediaPlayer.</p>
  
  <p>Thanks!</p>