= Playing a sound with QtMultimedia =

This example shows how to use the QAudioOutput class, introduced in Qt 4.6, to play a simple sine wave.

'''Warning:''' By default, the volume is set to zero because it is not possible to determine how loud the sound will be when played. Experiment carefully when playing sounds, especially if you are wearing headphones, to avoid causing damage to your hearing.

{{{
#!python

from math import pi, sin
import struct, sys

from PyQt4.QtCore import QBuffer, QByteArray, QIODevice, Qt
from PyQt4.QtGui import QApplication, QFormLayout, QLineEdit, QHBoxLayout, \
                        QPushButton, QSlider, QVBoxLayout, QWidget
from PyQt4.QtMultimedia import QAudio, QAudioDeviceInfo, QAudioFormat, QAudioOutput

class Window(QWidget):

    def __init__(self, parent = None):
    
        QWidget.__init__(self, parent)
        
        format = QAudioFormat()
        format.setChannels(1)
        format.setFrequency(22050)
        format.setSampleSize(16)
        format.setCodec("audio/pcm")
        format.setByteOrder(QAudioFormat.LittleEndian)
        format.setSampleType(QAudioFormat.SignedInt)
        self.output = QAudioOutput(format, self)
        
        self.frequency = 440
        self.volume = 0
        self.buffer = QBuffer()
        self.data = QByteArray()
        
        self.deviceLineEdit = QLineEdit()
        self.deviceLineEdit.setReadOnly(True)
        self.deviceLineEdit.setText(QAudioDeviceInfo.defaultOutputDevice().deviceName())
        
        self.pitchSlider = QSlider(Qt.Horizontal)
        self.pitchSlider.setMaximum(100)
        self.volumeSlider = QSlider(Qt.Horizontal)
        self.volumeSlider.setMaximum(32767)
        self.volumeSlider.setPageStep(1024)
        
        self.playButton = QPushButton(self.tr("&Play"))
        
        self.pitchSlider.valueChanged.connect(self.changeFrequency)
        self.volumeSlider.valueChanged.connect(self.changeVolume)
        self.playButton.clicked.connect(self.play)
        
        formLayout = QFormLayout()
        formLayout.addRow(self.tr("Device:"), self.deviceLineEdit)
        formLayout.addRow(self.tr("P&itch:"), self.pitchSlider)
        formLayout.addRow(self.tr("&Volume:"), self.volumeSlider)
        
        buttonLayout = QVBoxLayout()
        buttonLayout.addWidget(self.playButton)
        buttonLayout.addStretch()
        
        horizontalLayout = QHBoxLayout(self)
        horizontalLayout.addLayout(formLayout)
        horizontalLayout.addLayout(buttonLayout)
    
    def changeFrequency(self, value):
    
        self.frequency = 440 + (value * 2)
    
    def play(self):
    
        if self.output.state() == QAudio.ActiveState:
            self.output.stop()
        
        if self.buffer.isOpen():
            self.buffer.close()
        
        self.createData()
        
        self.buffer.setData(self.data)
        self.buffer.open(QIODevice.ReadOnly)
        self.buffer.seek(0)
        
        self.output.start(self.buffer)
    
    def changeVolume(self, value):
    
        self.volume = value
    
    def createData(self):
    
        # Create 2 seconds of data with 22050 samples per second, each sample
        # being 16 bits (2 bytes).
        
        self.data.clear()
        for i in xrange(2 * 22050):
            t = i / 22050.0
            value = int(self.volume * sin(2 * pi * self.frequency * t))
            self.data.append(struct.pack("<h", value))


if __name__ == "__main__":

    app = QApplication(sys.argv)
    window = Window()
    window.show()
    sys.exit(app.exec_())
}}}