How to show the current audio volume of my microphone? - audio

Question

I'm completely new to QMultimedia. At the moment, I try to get the audio stream from the microphone in my webcam for further processing. Right now I just try to continuously show the volume level of the sound "heard" by the mic with a slider. So I googled some code together (found nearly 10 tons of examples how I can play an audio, but only a few blocks of C++ code about audio input) and got stuck.
This is my actual code:
import sys, time
from PyQt4 import Qt, QtGui, QtCore, QtMultimedia
class VolumeSlider(QtGui.QSlider):
def __init__(self, parent=None):
super(VolumeSlider, self).__init__(parent)
self.audio = None
self.volumeSlider = QtGui.QSlider(QtCore.Qt.Horizontal)
self.volumeSlider.setTickInterval(1)
self.volumeSlider.setMaximum(100)
self.volumeSlider.setValue(49)
self.volumeSlider.show()
self.openMicStream()
# THIS IS WHAT I WANT - DOESN'T WORK
while True:
self.volumeSlider.setValue(self.audio.volume())
time.sleep(0.02)
def openMicStream( self ):
#audioInputDevices = QtMultimedia.QAudioDeviceInfo.availableDevices(QtMultimedia.QAudio.AudioInput)
#for d in audioInputDevices: d.deviceName()
info = QtMultimedia.QAudioDeviceInfo(QtMultimedia.QAudioDeviceInfo.defaultInputDevice())
print "Default audio input device:", info.deviceName()
audioFormat = QtMultimedia.QAudioFormat()
audioFormat.setFrequency(8000);
audioFormat.setChannels(1);
audioFormat.setSampleSize(8);
audioFormat.setCodec("audio/pcm");
audioFormat.setByteOrder(QtMultimedia.QAudioFormat.LittleEndian);
audioFormat.setSampleType(QtMultimedia.QAudioFormat.UnSignedInt);
audioDeviceInfo = QtMultimedia.QAudioDeviceInfo.defaultInputDevice();
if not audioDeviceInfo.isFormatSupported(audioFormat):
sys.stderr("default audioFormat not supported try to use nearest")
audioFormat = audioDeviceInfo.nearestFormat(audioFormat);
self.audioInput = QtMultimedia.QAudioInput(audioFormat);
fmtSupported = info.isFormatSupported(audioFormat)
print "Is the selected format supported?", fmtSupported
if not fmtSupported:
audioFormat = info.nearestFormat(audioFormat)
print "Is the nearest format supported?", info.isFormatSupported(audioFormat)
self.audio = QtMultimedia.QAudioInput(audioFormat, None)
self.audio.start()
if __name__ == "__main__":
app = Qt.QApplication(sys.argv)
x = VolumeSlider()
sys.exit(app.exec_())
Could anybody poke me in the head what I have to do at the "#THIS IS WHAT I WANT" place to calculate and show the current level of volume?

Answer 1

There is no inbuilt function for computing the current volume level of the input sound signal when recorded with QAudioInput neither in Qt 4 (QAudioInput documentation) nor in Qt 5.
But you could calculate it for yourself. The root-mean-square in a moving window of the signal is often used as a measure for current loudness. See How can I determine how loud a WAV file will sound? for more suggestions.

Answer 2

Solved it after a while of working on another parts. Now I can at least hear the sound out of the boxes, after I changed the openMicStream(self) to this:
def openMicStream( self ):
info = QAudioDeviceInfo(QAudioDeviceInfo.defaultInputDevice())
print "Default audioInput input device: ", info.deviceName()
audioFormat = QAudioFormat()
audioFormat.setFrequency(44100);
audioFormat.setChannels(1);
audioFormat.setSampleSize(16);
audioFormat.setCodec("audioInput/pcm");
audioFormat.setByteOrder(QAudioFormat.LittleEndian);
audioFormat.setSampleType(QAudioFormat.UnSignedInt);
audioDeviceInfo = QAudioDeviceInfo.defaultInputDevice();
if not audioDeviceInfo.isFormatSupported(audioFormat):
messages.error(__name__, "default audioFormat not supported try to use nearest")
audioFormat = audioDeviceInfo.nearestFormat(audioFormat);
print audioFormat.frequency()
print audioFormat.channels()
print audioFormat.sampleSize()
print audioFormat.codec()
print audioFormat.byteOrder()
print audioFormat.sampleType()
self.audioInput = QAudioInput(audioFormat);
audioFmtSupported = info.isFormatSupported(audioFormat)
messages.info(__name__, "Is the selected format supported?"+str(audioFmtSupported))
if not audioFmtSupported:
audioFormat = info.nearestFormat(audioFormat)
messages.info(__name__, "Is the nearest format supported?"+str(info.isFormatSupported(audioFormat)))
self.audioInput = QAudioInput(audioFormat, None)
self.audioOutput = QAudioOutput(audioFormat, None)
device = self.audioOutput.start()
self.audioInput.start(device)