QAudioOutput

The QAudioOutput class provides an interface for sending audio data to an audio output device. More…

Inheritance diagram of PySide2.QtMultimedia.QAudioOutput

Synopsis

Functions

Signals

Detailed Description

You can construct an audio output with the system’s default audio output device . It is also possible to create QAudioOutput with a specific QAudioDeviceInfo . When you create the audio output, you should also send in the QAudioFormat to be used for the playback (see the QAudioFormat class description for details).

To play a file:

Starting to play an audio stream is simply a matter of calling start() with a QIODevice . QAudioOutput will then fetch the data it needs from the io device. So playing back an audio file is as simple as:

    QFile sourceFile;   // class member.
    QAudioOutput* 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.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)), this, SLOT(handleStateChanged(QAudio::State)));
    audio->start(&sourceFile);
}

The file will start playing assuming that the audio system and output device support it. If you run out of luck, check what’s up with the error() function.

After the file has finished playing, we need to stop the device:

void AudioOutputExample::handleStateChanged(QAudio::State newState)
{
    switch (newState) {
        case QAudio::IdleState:
            // Finished playing (no more data)
            audio->stop();
            sourceFile.close();
            delete audio;
            break;

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

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

At any given time, the QAudioOutput will be in one of four states: active, suspended, stopped, or idle. These states are described by the State enum. State changes are reported through the stateChanged() signal. You can use this signal to, for instance, update the GUI of the application; the mundane example here being changing the state of a play/pause button. You request a state change directly with suspend() , stop() , reset() , resume() , and start() .

While the stream is playing, you can set a notify interval in milliseconds with setNotifyInterval() . This interval specifies the time between two emissions of the notify() signal. This is relative to the position in the stream, i.e., if the QAudioOutput is in the SuspendedState or the IdleState, the notify() signal is not emitted. A typical use-case would be to update a slider that allows seeking in the stream. If you want the time since playback started regardless of which states the audio output has been in, elapsedUSecs() is the function for you.

If an error occurs, you can fetch the error type with the error() function. Please see the Error enum for a description of the possible errors that are reported. When an error is encountered, the state changes to StoppedState . You can check for errors by connecting to the stateChanged() signal:

void AudioOutputExample::handleStateChanged(QAudio::State newState)
{
    switch (newState) {
        case QAudio::IdleState:
            // Finished playing (no more data)
            audio->stop();
            sourceFile.close();
            delete audio;
            break;

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

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

See also

QAudioInput QAudioDeviceInfo

class PySide2.QtMultimedia.QAudioOutput(audioDeviceInfo[, format=QAudioFormat()[, parent=None]])

PySide2.QtMultimedia.QAudioOutput([format=QAudioFormat()[, parent=None]])

param parent:

PySide2.QtCore.QObject

param audioDeviceInfo:

PySide2.QtMultimedia.QAudioDeviceInfo

param format:

PySide2.QtMultimedia.QAudioFormat

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

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

PySide2.QtMultimedia.QAudioOutput.bufferSize()
Return type:

int

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()

PySide2.QtMultimedia.QAudioOutput.bytesFree()
Return type:

int

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

Note

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

PySide2.QtMultimedia.QAudioOutput.category()
Return type:

str

Returns the audio category of this audio stream.

Some platforms can group audio streams into categories and manage their volumes independently, or display them in a system mixer control. You can set this property to allow the platform to distinguish the purpose of your streams.

See also

setCategory()

PySide2.QtMultimedia.QAudioOutput.elapsedUSecs()
Return type:

int

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

PySide2.QtMultimedia.QAudioOutput.error()
Return type:

Error

Returns the error state.

PySide2.QtMultimedia.QAudioOutput.format()
Return type:

PySide2.QtMultimedia.QAudioFormat

Returns the QAudioFormat being used.

PySide2.QtMultimedia.QAudioOutput.notify()
PySide2.QtMultimedia.QAudioOutput.notifyInterval()
Return type:

int

Returns the notify interval in milliseconds.

See also

setNotifyInterval()

PySide2.QtMultimedia.QAudioOutput.periodSize()
Return type:

int

Returns the period size in bytes. This is the amount of data required each period to prevent buffer underrun, and to ensure uninterrupted playback.

Note

It is recommended to provide at least enough data for a full period with each write operation.

PySide2.QtMultimedia.QAudioOutput.processedUSecs()
Return type:

int

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

PySide2.QtMultimedia.QAudioOutput.reset()

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

PySide2.QtMultimedia.QAudioOutput.resume()

Resumes processing audio data after a suspend() .

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

PySide2.QtMultimedia.QAudioOutput.setBufferSize(bytes)
Parameters:

bytes – int

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 - call bufferSize() anytime after start() to return the actual buffer size being used.

See also

bufferSize()

PySide2.QtMultimedia.QAudioOutput.setCategory(category)
Parameters:

category – str

Sets the audio category of this audio stream to category .

Some platforms can group audio streams into categories and manage their volumes independently, or display them in a system mixer control. You can set this property to allow the platform to distinguish the purpose of your streams.

Not all platforms support audio stream categorization. In this case, the function call will be ignored.

Changing an audio output stream’s category while it is opened will not take effect until it is reopened.

See also

category()

PySide2.QtMultimedia.QAudioOutput.setNotifyInterval(milliSeconds)
Parameters:

milliSeconds – int

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

See also

notifyInterval()

PySide2.QtMultimedia.QAudioOutput.setVolume(arg__1)
Parameters:

arg__1 – float

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 .

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

UI volume controls should usually be scaled nonlinearly. 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 convertVolume() for more details.

See also

volume()

PySide2.QtMultimedia.QAudioOutput.start(device)
Parameters:

device – PySide2.QtCore.QIODevice

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

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

See also

QIODevice

PySide2.QtMultimedia.QAudioOutput.start()
Return type:

PySide2.QtCore.QIODevice

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.

Note

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

If the QAudioOutput is able to access the system’s audio device, state() returns IdleState , error() returns NoError and the stateChanged() signal is emitted.

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

See also

QIODevice

PySide2.QtMultimedia.QAudioOutput.state()
Return type:

State

Returns the state of audio processing.

PySide2.QtMultimedia.QAudioOutput.stateChanged(state)
Parameters:

state – State

PySide2.QtMultimedia.QAudioOutput.stop()

Stops the audio output, detaching from the system resource.

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

PySide2.QtMultimedia.QAudioOutput.suspend()

Stops processing audio data, preserving buffered audio data.

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

PySide2.QtMultimedia.QAudioOutput.volume()
Return type:

float

Returns the volume between 0.0 and 1.0 inclusive.

See also

setVolume()