QAudioInput Class

Detailed Description

You can construct an audio input with the system's default audio input device. It is also possible to create QAudioInput with a specific QAudioDeviceInfo. When you create the audio input, you should also send in the QAudioFormat to be used for the recording (see the QAudioFormat class description for details).

To record to a file:

QAudioInput lets you record audio with an audio input device. The default constructor of this class will use the systems default audio device, but you can also specify a QAudioDeviceInfo for a specific device. You also need to pass in the QAudioFormat in which you wish to record.

Starting up the QAudioInput is simply a matter of calling start() with a QIODevice opened for writing. For instance, to record to a file, you can:

 QFile destinationFile;   // Class member
 QAudioInput* audio; // Class member
 {
     destinationFile.setFileName("/tmp/test.raw");
     destinationFile.open( QIODevice::WriteOnly | QIODevice::Truncate );

     QAudioFormat format;
     // Set up the desired format, for example:
     format.setSampleRate(8000);
     format.setChannelCount(1);
     format.setSampleSize(8);
     format.setCodec("audio/pcm");
     format.setByteOrder(QAudioFormat::LittleEndian);
     format.setSampleType(QAudioFormat::UnSignedInt);

     QAudioDeviceInfo info = QAudioDeviceInfo::defaultInputDevice();
     if (!info.isFormatSupported(format)) {
         qWarning() << "Default format not supported, trying to use the nearest.";
         format = info.nearestFormat(format);
     }

     audio = new QAudioInput(format, this);
     connect(audio, SIGNAL(stateChanged(QAudio::State)), this, SLOT(handleStateChanged(QAudio::State)));

     QTimer::singleShot(3000, this, SLOT(stopRecording()));
     audio->start(&destinationFile);
     // Records audio for 3000ms
 }

This will start recording if the format specified is supported by the input device (you can check this with QAudioDeviceInfo::isFormatSupported(). In case there are any snags, use the error() function to check what went wrong. We stop recording in the stopRecording() slot.

 void AudioInputExample::stopRecording()
 {
     audio->stop();
     destinationFile.close();
     delete audio;
 }

At any point in time, QAudioInput will be in one of four states: active, suspended, stopped, or idle. These states are specified by the QAudio::State enum. You can request a state change directly through suspend(), resume(), stop(), reset(), and start(). The current state is reported by state(). QAudioOutput will also signal you when the state changes (stateChanged()).

QAudioInput provides several ways of measuring the time that has passed since the start() of the recording. The processedUSecs() function returns the length of the stream in microseconds written, i.e., it leaves out the times the audio input was suspended or idle. The elapsedUSecs() function returns the time elapsed since start() was called regardless of which states the QAudioInput has been in.

If an error should occur, you can fetch its reason with error(). The possible error reasons are described by the QAudio::Error enum. The QAudioInput will enter the StoppedState when an error is encountered. Connect to the stateChanged() signal to handle the error:

 void AudioInputExample::handleStateChanged(QAudio::State newState)
 {
     switch (newState) {
         case QAudio::StoppedState:
             if (audio->error() != QAudio::NoError) {
                 // Error handling
             } else {
                 // Finished recording
             }
             break;

         case QAudio::ActiveState:
             // Started recording - read from IO device
             break;

         default:
             // ... other cases as appropriate
             break;
     }
 }