QAudioOutput¶
- PyQt5.QtMultimedia.QAudioOutput
Inherits from QObject.
Description¶
The QAudioOutput class provides an interface for sending audio data to an audio output device.
You can construct an audio output with the system’s defaultOutputDevice(). 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 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
Methods¶
- __init__(format: QAudioFormat = QAudioFormat(), parent: QObject = None)
Construct a new audio output and attach it to parent. The default audio output device is used with the output format parameters.
- __init__(QAudioDeviceInfo, format: QAudioFormat = QAudioFormat(), parent: QObject = None)
Construct a new audio output and attach it to parent. The device referenced by audioDevice is used with the output format parameters.
- bufferSize() → 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
- bytesFree() → 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.
- category() → 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
- elapsedUSecs() → int
Returns the microseconds since start() was called, including time in Idle and Suspend states.
- error() → Error
Returns the error state.
- format() → QAudioFormat
Returns the QAudioFormat being used.
- notifyInterval() → int
Returns the notify interval in milliseconds.
See also
- periodSize() → 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.
- processedUSecs() → 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.
- setBufferSize(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
- setCategory(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
- setNotifyInterval(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
- setVolume(float)
Sets the output volume to volume.
The volume is scaled linearly from
0.0(silence) to1.0(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
- start() → 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
- start(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
- state() → State
Returns the state of audio processing.
- stop()
Stops the audio output, 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 emits stateChanged signal.
- volume() → float
Returns the volume between 0.0 and 1.0 inclusive.
See also
