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QAudioInput Class Reference
^{^{[QtMultimedia module]}}

The QAudioInput class provides an interface for receiving audio data from an audio input device. More...

Inherits QObject.

Methods

__init__ (self, QAudioFormat format = QAudioFormat(), QObject parent = None)
__init__ (self, QAudioDeviceInfo audioDevice, QAudioFormat format = QAudioFormat(), QObject parent = None)
int bufferSize (self)
int bytesReady (self)
int elapsedUSecs (self)
QAudio.Error error (self)
QAudioFormat format (self)
int notifyInterval (self)
int periodSize (self)
int processedUSecs (self)
reset (self)
resume (self)
setBufferSize (self, int bytes)
setNotifyInterval (self, int milliSeconds)
start (self, QIODevice device)
QIODevice start (self)
QAudio.State state (self)
stop (self)
suspend (self)

Qt Signals

void notify ()
void stateChanged (QAudio::State)

Detailed Description

The QAudioInput class provides an interface for receiving audio data from an audio input device.

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 outputFile;         // class member.
     QAudioInput *audioInput;  // class member.
     ...
     void startRecording()
     {
         outputFile.setFileName("/tmp/test.raw");
         outputFile.open( QIODevice.WriteOnly | QIODevice.Truncate );

         QAudioFormat format;
         // set up the format you want, eg.
         format.setFrequency(8000);
         format.setChannels(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 try to use nearest";
             format = info.nearestFormat(format);
         }

         audioInput = new QAudioInput(format, this);
         QTimer.singleShot(3000, this, SLOT(stopRecording()));
         audioInput->start(&outputFile);
         // 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 stopRecording()
     {
         audioInput->stop();
         outputFile.close();
         delete audioInput;
     }

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 stateChanged(QAudio.State newState)
     {
         switch(newState) {
             case QAudio.StoppedState:
             if (audioInput->error() != QAudio.NoError) {
                  // Perform error handling
             } else {

             }
             break;

Symbian Platform Security Requirements

On Symbian, processes which use this class must have the UserEnvironment platform security capability. If the client process lacks this capability, calls to either overload of start() will fail. This failure is indicated by the QAudioInput object setting its error() value to QAudio.OpenError and then emitting a stateChanged(QAudio.StoppedState) signal.

Platform security capabilities are added via the TARGET.CAPABILITY qmake variable.

Method Documentation

QAudioInput.init (self, QAudioFormat format = QAudioFormat(), QObject parent = None)

The parent argument, if not None, causes self to be owned by Qt instead of PyQt.

Construct a new audio input and attach it to parent. The default audio input device is used with the output format parameters.

QAudioInput.init (self, QAudioDeviceInfo audioDevice, QAudioFormat format = QAudioFormat(), QObject parent = None)

The parent argument, if not None, causes self to be owned by Qt instead of PyQt.

Construct a new audio input and attach it to parent. The device referenced by audioDevice is used with the input format parameters.

int QAudioInput.bufferSize (self)

Returns the audio buffer size in milliseconds.

If called before start(), returns platform default value. If called before start() but setBufferSize() was called prior, returns value set by setBufferSize(). If called after start(), returns the actual buffer size being used. This may not be what was set previously by setBufferSize().

See also setBufferSize().

int QAudioInput.bytesReady (self)

Returns the amount of audio data available to read in bytes.

NOTE: returned value is only valid while in QAudio.ActiveState or QAudio.IdleState state, otherwise returns zero.

int QAudioInput.elapsedUSecs (self)

Returns the microseconds since start() was called, including time in Idle and Suspend states.

QAudio.Error QAudioInput.error (self)

Returns the error state.

QAudioFormat QAudioInput.format (self)

Returns the QAudioFormat being used.

int QAudioInput.notifyInterval (self)

Returns the notify interval in milliseconds.

See also setNotifyInterval().

int QAudioInput.periodSize (self)

Returns the period size in bytes.

Note: This is the recommended read size in bytes.

Sets error() to QAudio.NoError. Sets state() to QAudio.ActiveState if you previously called start(QIODevice*). Sets state() to QAudio.IdleState if you previously called start(). emits stateChanged() signal.

QAudioInput.setBufferSize (self, int bytes)

Sets the audio buffer size to value milliseconds.

Note: This function can be called anytime before start(), calls to this are ignored after start(). It should not be assumed that the buffer size set is the actual buffer size used, calling bufferSize() anytime after start() will return the actual buffer size being used.

See also bufferSize().

QAudioInput.setNotifyInterval (self, int milliSeconds)

Sets the interval for notify() signal to be emitted. This is based on the ms of audio data processed not on actual real-time. The minimum resolution of the timer is platform specific and values should be checked with notifyInterval() to confirm actual value being used.

See also notifyInterval().

QAudioInput.start (self, QIODevice device)

Uses the device as the QIODevice to transfer data. Passing a QIODevice allows the data to be transferred without any extra code. All that is required is to open the QIODevice. QAudioInput does not take ownership of device.

The QAudioInput will write to the device when new data is available. You can subclass QIODevice and reimplement writeData() if you wish to access the data. If you simply want to save data to a file, you can pass a QFile to this function.

If able to successfully get audio data from the systems audio device the state() is set to either QAudio.ActiveState or QAudio.IdleState, error() is set to QAudio.NoError and the stateChanged() signal is emitted.

If a problem occurs during this process the error() is set to QAudio.OpenError, state() is set to QAudio.StoppedState and stateChanged() signal is emitted.

QAudioInput#Symbian Platform Security Requirements

See also QIODevice.

QIODevice QAudioInput.start (self)

Returns a pointer to a new QIODevice that will be used to handle the data transfer. This QIODevice can be used to read() audio data directly. You will typically connect to the readyRead() signal, and read from the device in the slot you connect to. QAudioInput keeps ownership of the device.

If able to access the systems audio device the state() is set to QAudio.IdleState, error() is set to QAudio.NoError and the stateChanged() signal is emitted.

If a problem occurs during this process the error() is set to QAudio.OpenError, state() is set to QAudio.StoppedState and stateChanged() signal is emitted.

QAudioInput#Symbian Platform Security Requirements

See also QIODevice.