QAudioSource Class

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

Header: #include <QAudioSource>
CMake: find_package(Qt6 COMPONENTS Multimedia REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Multimedia)
qmake: QT += multimedia
Inherits: QObject

Public Functions

QAudioSource(const QAudioDevice &audioDevice, const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr)
QAudioSource(const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr)
virtual ~QAudioSource()
qsizetype bufferSize() const
qsizetype bytesAvailable() const
qint64 elapsedUSecs() const
QAudio::Error error() const
QAudioFormat format() const
qint64 processedUSecs() const
void reset()
void resume()
void setBufferSize(qsizetype value)
void setVolume(qreal volume)
void start(QIODevice *device)
QIODevice *start()
QAudio::State state() const
void stop()
void suspend()
qreal volume() const

Signals

void stateChanged(QAudio::State state)

Detailed Description

You can construct an audio input with the system's default audio input device. It is also possible to create QAudioSource with a specific QAudioDevice. 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:

QAudioSource 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 QAudioDevice for a specific device. You also need to pass in the QAudioFormat in which you wish to record.

Starting up the QAudioSource 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
QAudioSource* 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.setSampleFormat(QAudioFormat::UInt8);

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

    audio = new QAudioSource(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 QAudioDevice::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, QAudioSource 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(). QAudioSink will also signal you when the state changes (stateChanged()).

QAudioSource 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 QAudioSource 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 QAudioSource 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;
    }
}

See also QAudioSink and QAudioDevice.

Member Function Documentation

QAudioSource::QAudioSource(const QAudioDevice &audioDevice, const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr)

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

QAudioSource::QAudioSource(const QAudioFormat &format = QAudioFormat(), QObject *parent = nullptr)

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

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

This signal is emitted when the device state has changed.

[virtual] QAudioSource::~QAudioSource()

Destroy this audio input.

qsizetype QAudioSource::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 QAudioSource::bytesAvailable() 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 QAudioSource::elapsedUSecs() const

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

QAudio::Error QAudioSource::error() const

Returns the error state.

QAudioFormat QAudioSource::format() const

Returns the QAudioFormat being used.

qint64 QAudioSource::processedUSecs() const

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

void QAudioSource::reset()

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

void QAudioSource::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 QAudioSource::setBufferSize(qsizetype value)

Sets the audio buffer size to value 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 QAudioSource::setVolume(qreal volume)

Sets the input volume to volume.

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

If the device does not support adjusting the input volume then volume will be ignored and the input volume will remain at 1.0.

The default volume is 1.0.

Note: Adjustments to the volume will change the volume of this audio stream, not the global volume.

See also volume().

void QAudioSource::start(QIODevice *device)

Starts transferring audio data from the system's audio input to the device. The device must have been opened in the WriteOnly, Append or ReadWrite modes.

If the QAudioSource is able to successfully get audio data, state() returns either QAudio::ActiveState or QAudio::IdleState, error() returns QAudio::NoError and the stateChanged() signal is emitted.

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

See also QIODevice.

QIODevice *QAudioSource::start()

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

Note: The pointer will become invalid after the stream is stopped or if you start another stream.

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

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

See also QIODevice.

QAudio::State QAudioSource::state() const

Returns the state of audio processing.

void QAudioSource::stop()

Stops the audio input, detaching from the system resource.

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

void QAudioSource::suspend()

Stops processing audio data, preserving buffered audio data.

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

qreal QAudioSource::volume() const

Returns the input volume.

If the device does not support adjusting the input volume the returned value will be 1.0.

See also setVolume().

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