QAudioInput Class Reference

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

 #include <QAudioInput>

Inherits: QObject.

This class was introduced in Qt 4.6.

Public Functions

QAudioInput ( const QAudioFormat & format = QAudioFormat(), QObject * parent = 0 )
QAudioInput ( const QAudioDeviceInfo & audioDevice, const QAudioFormat & format = QAudioFormat(), QObject * parent = 0 )
~QAudioInput ()
int bufferSize () const
int bytesReady () const
qint64 elapsedUSecs () const
QAudio::Error error () const
QAudioFormat format () const
int notifyInterval () const
int periodSize () const
qint64 processedUSecs () const
void reset ()
void resume ()
void setBufferSize ( int value )
void setNotifyInterval ( int ms )
void start ( QIODevice * device )
QIODevice * start ()
QAudio::State state () const
void stop ()
void suspend ()
  • 29 public functions inherited from QObject

Signals

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

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 7 static public members inherited from QObject
  • 8 protected functions inherited from QObject

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.

See also QAudioOutput and QAudioDeviceInfo.

Member Function Documentation

QAudioInput::QAudioInput ( const QAudioFormat & format = QAudioFormat(), QObject * parent = 0 )

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

QAudioInput::QAudioInput ( const QAudioDeviceInfo & audioDevice, const QAudioFormat & format = QAudioFormat(), QObject * parent = 0 )

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

QAudioInput::~QAudioInput ()

Destroy this audio input.

int QAudioInput::bufferSize () const

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 () const

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.

qint64 QAudioInput::elapsedUSecs () const

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

QAudio::Error QAudioInput::error () const

Returns the error state.

QAudioFormat QAudioInput::format () const

Returns the QAudioFormat being used.

void QAudioInput::notify () [signal]

This signal is emitted when x ms of audio data has been processed the interval set by setNotifyInterval(x).

int QAudioInput::notifyInterval () const

Returns the notify interval in milliseconds.

See also setNotifyInterval().

int QAudioInput::periodSize () const

Returns the period size in bytes.

Note: This is the recommended read size in bytes.

qint64 QAudioInput::processedUSecs () const

Returns the amount of audio data processed since start() was called in microseconds.

void QAudioInput::reset ()

Drops all audio data in the buffers, resets buffers to zero.

void QAudioInput::resume ()

Resumes processing audio data after a suspend().

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.

void QAudioInput::setBufferSize ( int value )

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().

void QAudioInput::setNotifyInterval ( int ms )

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().

void QAudioInput::start ( 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 ()

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.

QAudio::State QAudioInput::state () const

Returns the state of audio processing.

void QAudioInput::stateChanged ( QAudio::State state ) [signal]

This signal is emitted when the device state has changed.

void QAudioInput::stop ()

Stops the audio input, detaching from the system resource.

Sets error() to QAudio::NoError, state() to QAudio::StoppedState and emit stateChanged() signal.

void QAudioInput::suspend ()

Stops processing audio data, preserving buffered audio data.

Sets error() to QAudio::NoError, state() to QAudio::SuspendedState and emit stateChanged() signal.

Notes provided by the Qt Community
Informative
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Votes: 0

Coverage: Qt library 4.7, 4.8, 5.0

Picture of JKSH JKSH

Area 51 Engineer
1 note

bufferSize() and setBufferSize() gets and sets BYTES, not milliseconds

This is fixed for the Qt 5.0 release, but the old versions of the docs contain this error.

See QTBUG-26600 [bugreports.qt-project.org]

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