Crossfading audio with PyQT4 and Phonon

I'm trying to get audio files to crossfade with phonon. I'm using PyQT4. I have tracks queuing properly, but I'm stuck with the fade effect. I think I need to be using the KVolumeFader effect. Here's my current code:

def music_play(self):
    self.delayedInit()
    self.m_media.setCurrentSource(Phonon.MediaSource(self.playlist[self.playlist_pos]))
    self.m_media.play()

def music_stop(self):
    self.m_media.stop()

def delayedInit(self):
    if not self.m_media:
        self.m_media = Phonon.MediaObject(self)
        audioOutput = Phonon.AudioOutput(Phonon.MusicCategory, self)
        Phonon.createPath(self.m_media, audioOutput)

def enqueueNextSource(self):
    if len(self.playlist) >= self.playlist_pos+1:
        self.playlist_pos += 1
        self.m_media.enqueue(Phonon.MediaSource(self.playlist[self.playl开发者_运维技巧ist_pos]))
    else:
        self.m_media.stop()

Can anyone give me some advice on implementing the effect?

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Seems I found the solution I was looking for. Although it's not supported by every phonon backend, setting the MediaObject's transitionTime with a negative number will crossfade.