QAudioOutput Class Reference

 #include <QAudioOutput>

 QFile inputFile;     // class member.
 QAudioOutput* audio; // class member.

 inputFile.setFileName("/tmp/test.raw");
 inputFile.open(QIODevice::ReadOnly);

 QAudioFormat format;
 // Set up the format, 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::defaultOutputDevice());
 if (!info.isFormatSupported(format)) {
     qWarning()<<"raw audio format not supported by backend, cannot play audio.";
     return;
 }

 audio = new QAudioOutput(format, this);
 connect(audio,SIGNAL(stateChanged(QAudio::State)),SLOT(finishedPlaying(QAudio::State)));
 audio->start(&inputFile);

 void finishedPlaying(QAudio::State state)
 {
   if(state == QAudio::IdleState) {
     audio->stop();
     inputFile.close();
     delete audio;
   }
 }

     void stateChanged(QAudio::State newState)
     {
         switch (newState) {
             case QAudio::StopState:
                 if (output->error() != QAudio::NoError) {
                     // Perform error handling
                 } else {
                     // Normal stop
                 }
                 break;

Member Function Documentation

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

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

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

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

QAudioOutput::~QAudioOutput ()

Destroys this audio output.

int QAudioOutput::bufferSize () const

Returns the audio buffer size in bytes.

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 QAudioOutput::bytesFree () const

Returns the free space available in bytes in the audio buffer.

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

qint64 QAudioOutput::elapsedUSecs () const

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

QAudio::Error QAudioOutput::error () const

Returns the error state.

QAudioFormat QAudioOutput::format () const

Returns the QAudioFormat being used.

void QAudioOutput::notify () [signal]

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

int QAudioOutput::notifyInterval () const

Returns the notify interval in milliseconds.

See also setNotifyInterval().

int QAudioOutput::periodSize () const

Returns the period size in bytes.

Note: This is the recommended write size in bytes.

qint64 QAudioOutput::processedUSecs () const

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

Note: The amount of audio data played can be determined by subtracting the microseconds of audio data still in the systems audio buffer.

 qint64 bytesInBuffer = bufferSize() - bytesFree();
 qint64 usInBuffer = (qint64)(1000000) * bytesInBuffer / ( channels() * sampleSize() / 8 ) / frequency();
 qint64 usPlayed = processedUSecs() - usInBuffer;

void QAudioOutput::reset ()

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

void QAudioOutput::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.

Note: signal will always be emitted during execution of the resume() function.

void QAudioOutput::setBufferSize ( int value )

Sets the audio buffer size to value in bytes.

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 QAudioOutput::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 QAudioOutput::start ( QIODevice * device )

Uses the device as the QIODevice to transfer data. Passing a QIODevice allows the data to be transfered without any extra code. All that is required is to open the QIODevice.

If able to successfully output audio data to the systems audio device the state() is set to QAudio::ActiveState, 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.

In either case, the stateChanged() signal may be emitted either synchronously during execution of the start() function or asynchronously after start() has returned to the caller.

See also QIODevice.

QIODevice * QAudioOutput::start ()

Returns a pointer to the QIODevice being used to handle the data transfer. This QIODevice can be used to write() audio data directly.

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.

In either case, the stateChanged() signal may be emitted either synchronously during execution of the start() function or asynchronously after start() has returned to the caller.

See also QIODevice.

QAudio::State QAudioOutput::state () const

Returns the state of audio processing.

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

This signal is emitted when the device state has changed. This is the current state of the audio output.

void QAudioOutput::stop ()

Stops the audio output, detaching from the system resource.

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

void QAudioOutput::suspend ()

Stops processing audio data, preserving buffered audio data.

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