PySide6.QtMultimedia.QAudioSource¶

class QAudioSource¶

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

Synopsis¶

Methods¶

def __init__()
def bufferFrameCount()
def bufferSize()
def bytesAvailable()
def elapsedUSecs()
def error()
def format()
def framesAvailable()
def isNull()
def processedUSecs()
def reset()
def resume()
def setBufferFrameCount()
def setBufferSize()
def setVolume()
def start()
def state()
def stop()
def suspend()
def volume()

Signals¶

def stateChanged()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description¶

Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

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).

QAudioSink can be used in two different modes:

Using a QIODevice from an application thread

Using a callback-based interface from the audio thread

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.OpenModeFlag.WriteOnly | QIODevice.Truncate )
format = QAudioFormat()
# Set up the desired format, for example:
format.setSampleRate(44100)
format.setChannelCount(1)
format.setSampleFormat(QAudioFormat.Int16)
info = QMediaDevices.defaultAudioInput()
if not info.isFormatSupported(format):
    qWarning() << "Default format not supported, trying to use the nearest."

audio = QAudioSource(format, self)
audio.stateChanged.connect(self.handleStateChanged)
QTimer::singleShot(3000, self.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 isFormatSupported() . In case there are any snags, use the error() function to check what went wrong. We stop recording in the stopRecording() slot.

def stopRecording(self):

    audio.stop()
    destinationFile.close()
    del 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 State enum.

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.

The QIODevice interface is designed to be used from the application thread. A wait-free ringbuffer is used to communicate to the audio thread. The size of this ringbuffer can be configured with setBufferSize() and defaults to 250ms. The state of this buffer can be queried with bytesFree(). If the ringbuffer is full because the application does not read from the QIODevice in time, the state will change to IdleState and resume to ActiveState once the application has read data from the QIODevice. Note that this state change will drop audio data, so you should always read from the QIODevice as fast as possible to avoid dropouts.

The preferred way to achieve low audio latencies is to use the callback based interface. It allows you to read audio data directly from the audio device without having to go through a QIODevice. This is done by calling start() with a callback function that will be called from the audio thread. This callback function will be called with a QSpan<const SampleType> whenever the audio backend produces data.

QAudioSource* audio # class member.
std.atomic<float> peakLevel # class member.
format = QAudioFormat()
# Set up the format, eg.
format.setSampleRate(44100)
format.setChannelCount(2)
format.setSampleFormat(QAudioFormat.Float)
info = QAudioDevice(QMediaDevices.defaultAudioOutput())
if not info.isFormatSupported(format):
    qWarning() << "Raw audio format not supported by backend, cannot capture audio."
    return

audio = QAudioSource(format, self)
audio.start([peakLevel] (QSpan<float> interleavedAudioBuffer) {
    level = peakLevel.load()
    for sample in interleavedAudioBuffer:
        # Calculate the peak level from the audio samples
        level = std.max(level, std.abs(sample))

    peakLevel.store(level)
    # Note: care needs to be taken if the application thread needs to be notified, as the
    # audio callback should not use any potentially blocking system calls.
    # Good options are autoreset events (windows), eventfd (linux) or kqueue/EVFILT_USER on macos.
})
if not audio.error() == QtAudio.Error.NoError:
    # in addition to the other start() signatures, starting the audio callback will fail if
    # * the backend does not implement callback-based IO (the API is available on all major
    #   platforms)
    # * the signature of the audio callback does not match format.sampleFormat()
    qWarning() << "Error starting audio output:" << audio.errorString()

Unlike the QIODevice-based interface, the QAudioSource can only be in the states active, suspendend and stopped. The setBufferSize() API is not available when using the callback, the size of the callback argument is determined by the audio backend.

Note

This API is only available on platforms that support the callback API: Apple’s CoreAudio (macOS, iOS, etc), Windows, Linux (using the PulseAudio or PipeWire backend) and Android.

Note

The callback will be called on a soft-realtime audio thread. It is important to ensure that the callback does not block, as this can cause audio glitches or dropouts. This includes performing blocking IO, locking mutexes, allocating memories or any other operations that may block. For best practices consult Ross Bencina’s article Real-time audio programming 101: time waits for nothing . Also consider using clang’s Realtime sanitizer to validate the audio callback.

State changes are reported through the stateChanged() signal. You can request a state change directly through suspend() , resume() , stop() , reset() , and start() .

The QAudioSource will enter the StoppedState when an error is encountered. The error type can be retrieved error() function. Please see the Error enum for a description of the possible errors that are reported. Calling stop() or reset() will reset the error state to NoError .

def handleStateChanged(self, newState):

    match newState:
            case QtAudio.StoppedState:
                if audio.error() != QtAudio.NoError:
                # Error handling
                else:
                # Finished recording


            case QtAudio.ActiveState:
            # Started recording - read from IO device

            case _:
            # ... other cases as appropriate

See also

QAudioSink QAudioDevice

__init__([format=QAudioFormat()[, parent=None]])¶

Parameters:

format – QAudioFormat
parent – QObject

Construct a new audio input and attach it to parent. The default audio input device is used with the output format parameters. If format is default-initialized, the format will be set to the preferred format of the audio device.

__init__(audioDeviceInfo[, format=QAudioFormat()[, parent=None]])

Parameters:

audioDeviceInfo – QAudioDevice
format – QAudioFormat
parent – QObject

Construct a new audio input and attach it to parent. The device referenced by audioDevice is used with the input format parameters. If format is default-initialized, the format will be set to the preferred format of audioDevice.

bufferFrameCount()¶

Return type:: int

Returns the audio buffer size in frames.

If called before start() , returns platform default value. If called before start() but setBufferSize() or setBufferFrameCount() was called prior, returns value set by setBufferSize() or setBufferFrameCount(). If called after start(), returns the actual buffer size being used. This may not be what was set previously by setBufferSize() or setBufferFrameCount().

See also

setBufferFrameCount() bufferSize

bufferSize()¶

Return type:: int

Returns the audio buffer size in bytes.

See also

setBufferSize() bufferFrameCount

bytesAvailable()¶

Return type:: int

Returns the amount of audio data available to read in bytes.

Note

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

See also

framesAvailable

elapsedUSecs()¶

Return type:: int

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

error()¶

Return type:: Error

Returns the error state.

format()¶

Return type:: QAudioFormat

Returns the QAudioFormat being used.

framesAvailable()¶

Return type:: int

Returns the amount of audio data available to read in frames.

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

See also

bytesAvailable

isNull()¶

Return type:: bool

Returns true if the audio source is null, otherwise returns false.

processedUSecs()¶

Return type:: int

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

reset()¶

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

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.

setBufferFrameCount(frames)¶

Parameters:: frames – int

Sets the audio buffer size to value in frame count.

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 bufferFrameCount() anytime after start() to return the actual buffer size being used.

See also

bufferFrameCount() setBufferSize

setBufferSize(bytes)¶

Parameters:: bytes – int

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() setBufferFrameCount

setVolume(volume)¶

Parameters:: volume – float

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()

start()¶

Return type:: QIODevice

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 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 interface

start(device)

Parameters:: device – QIODevice

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 ActiveState or 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 interface

state()¶

Return type:: State

Returns the state of audio processing.

stateChanged(state)¶

Parameters:: state – State

This signal is emitted when the device state has changed.

Note

The QtAudio namespace was named QAudio up to and including Qt 6.6. String-based connections to this signal have to use QAudio::State as the parameter type: connect(source, SIGNAL(stateChanged(QAudio::State)), ...);

stop()¶

Stops the audio input, detaching from the system resource.

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

suspend()¶

Stops processing audio data, preserving buffered audio data.

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

volume()¶

Return type:: float

Returns the input volume.

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

See also

setVolume()