sample code:
Qt Code: 
  1. audioOutput = new Phonon::AudioOutput(Phonon::VideoCategory, this);
  2.     volumeSlider = new Phonon::VolumeSlider(ui->frame_2);
  3.     volumeSlider->setObjectName(QString::fromUtf8("volumeSlider"));
  4.     volumeSlider->setStyleSheet("border:none;background:none;");
  5.     volumeSlider->setGeometry(QRect(105,70,141, 50));
  6.     mediaObject = new Phonon::MediaObject(this);
  7.     mediaObject->setCurrentSource(Phonon::MediaSource(musicpath));
  8.     mediaObject->setPrefinishMark(300);
  9.     mediaObject->setTransitionTime(0);
  10.     connect(mediaObject, SIGNAL(prefinishMarkReached(qint32)), SLOT(nextSource1(qint32)));
  11.      Phonon::createPath(mediaObject, audioOutput);
  12.     volumeSlider->setAudioOutput(audioOutput);
  13.  
  14. /////////////////////////////////////////////////////////
  15.  
  16. void MainWindow::nextSource1(qint32)
  17. {
  18.     mediaObject->seek(0);
  19. }
To copy to clipboard, switch view to plain text mode 

now there is a delay below one second..
we want to play a sound without any delay(gapless playback)
please help me to avoid this problem...I am new in QT ...i am using QT 4.7.4,developing QT GUI application...