QAudioSink Class

QFile sourceFile;   // class member.
QAudioSink* audio; // class member.
{
    sourceFile.setFileName("/tmp/test.raw");
    sourceFile.open(QIODevice::ReadOnly);

    QAudioFormat format;
    // Set up the format, eg.
    format.setSampleRate(8000);
    format.setChannelCount(1);
    format.setSampleFormat(QAudioFormat::UInt8);

    QAudioDevice info(QMediaDevices::defaultAudioOutput());
    if (!info.isFormatSupported(format)) {
        qWarning() << "Raw audio format not supported by backend, cannot play audio.";
        return;
    }

    audio = new QAudioSink(format, this);
    connect(audio, QAudioSink::stateChanged, this, &AudioInputExample::handleStateChanged);
    audio->start(&sourceFile);
}

void AudioOutputExample::stopAudioOutput()
{
    audio->stop();
    sourceFile.close();
    delete audio;
}

void AudioOutputExample::handleStateChanged(QAudio::State newState)
{
    switch (newState) {
        case QAudio::IdleState:
            // Finished playing (no more data)
            AudioOutputExample::stopAudioOutput();
            break;

        case QAudio::StoppedState:
            // Stopped for other reasons
            if (audio->error() != QAudio::NoError) {
                // Error handling
            }
            break;

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

Member Function Documentation

[explicit] QAudioSink::QAudioSink(const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr)

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

[explicit] QAudioSink::QAudioSink(const QAudioDevice &audioDevice, const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr)

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

[virtual noexcept] QAudioSink::~QAudioSink()

Destroys this audio output.

This will release any system resources used and free any buffers.

qsizetype QAudioSink::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().

qsizetype QAudioSink::bytesFree() const

Returns the number of free bytes available in the audio buffer.

qint64 QAudioSink::elapsedUSecs() const

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

QtAudio::Error QAudioSink::error() const

Returns the error state.

QAudioFormat QAudioSink::format() const

Returns the QAudioFormat being used.

bool QAudioSink::isNull() const

Returns true is the QAudioSink instance is null, otherwise returns false.

qint64 QAudioSink::processedUSecs() const

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

void QAudioSink::reset()

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

void QAudioSink::resume()

Resumes processing audio data after a suspend().

Sets state() to the state the sink had when suspend() was called, and sets error() to QAudioError::NoError. This function does nothing if the audio sink's state is not QtAudio::SuspendedState.

void QAudioSink::setBufferSize(qsizetype value)

Sets the audio buffer size to value in bytes.

See also bufferSize().

void QAudioSink::setVolume(qreal volume)

Sets the output volume to volume.

The volume is scaled linearly from 0.0 (silence) to 1.0 (full volume). Values outside this range will be clamped.

The default volume is 1.0.

UI volume controls should usually be scaled non-linearly. For example, using a logarithmic scale will produce linear changes in perceived loudness, which is what a user would normally expect from a volume control. See QtAudio::convertVolume() for more details.

See also volume().

void QAudioSink::start(QIODevice *device)

Starts transferring audio data from the device to the system's audio output. The device must have been opened in the ReadOnly or ReadWrite modes.

If the QAudioSink is able to successfully output audio data, state() returns QtAudio::ActiveState, error() returns QtAudio::NoError and the stateChanged() signal is emitted.

If a problem occurs during this process, error() returns QtAudio::OpenError, state() returns QtAudio::StoppedState and the stateChanged() signal is emitted.

See also QIODevice.

QIODevice *QAudioSink::start()

Returns a pointer to the internal QIODevice being used to transfer data to the system's audio output. The device will already be open and write() can write data directly to it.

If the QAudioSink is able to access the system's audio device, state() returns QtAudio::IdleState, error() returns QtAudio::NoError and the stateChanged() signal is emitted.

If a problem occurs during this process, error() returns QtAudio::OpenError, state() returns QtAudio::StoppedState and the stateChanged() signal is emitted.

See also QIODevice.

QtAudio::State QAudioSink::state() const

Returns the state of audio processing.

[signal] void QAudioSink::stateChanged(QtAudio::State state)

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

void QAudioSink::stop()

Stops the audio output, detaching from the system resource.

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

See also reset().

void QAudioSink::suspend()

Stops processing audio data, preserving buffered audio data.

Sets error() to QtAudio::NoError, state() to QtAudio::SuspendedState and emits stateChanged() signal.

qreal QAudioSink::volume() const

Returns the volume between 0.0 and 1.0 inclusive.

See also setVolume().