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QAudio Namespace

The QAudio namespace contains enums used by the audio classes. More...

Header: #include <QAudio>
qmake: QT += multimedia

    Types

    enum Error { NoError, OpenError, IOError, UnderrunError, FatalError }
    enum Mode { AudioOutput, AudioInput }
    enum Role { UnknownRole, MusicRole, VideoRole, VoiceCommunicationRole, ..., CustomRole }
    enum State { ActiveState, SuspendedState, StoppedState, IdleState, InterruptedState }
    enum VolumeScale { LinearVolumeScale, CubicVolumeScale, LogarithmicVolumeScale, DecibelVolumeScale }

    Functions

    qreal convertVolume(qreal volume, QAudio::VolumeScale from, QAudio::VolumeScale to)

    Detailed Description

    The QAudio namespace contains enums used by the audio classes.

    Type Documentation

    enum QAudio::Error

    Constant Value Description
    QAudio::NoError 0 No errors have occurred
    QAudio::OpenError 1 An error occurred opening the audio device
    QAudio::IOError 2 An error occurred during read/write of audio device
    QAudio::UnderrunError 3 Audio data is not being fed to the audio device at a fast enough rate
    QAudio::FatalError 4 A non-recoverable error has occurred, the audio device is not usable at this time.

    enum QAudio::Mode

    Constant Value Description
    QAudio::AudioOutput 1 audio output device
    QAudio::AudioInput 0 audio input device

    enum QAudio::Role

    This enum describes the role of an audio stream.

    Constant Value Description
    QAudio::UnknownRole 0 The role is unknown or undefined
    QAudio::MusicRole 1 Music
    QAudio::VideoRole 2 Soundtrack from a movie or a video
    QAudio::VoiceCommunicationRole 3 Voice communications, such as telephony
    QAudio::AlarmRole 4 Alarm
    QAudio::NotificationRole 5 Notification, such as an incoming e-mail or a chat request
    QAudio::RingtoneRole 6 Ringtone
    QAudio::AccessibilityRole 7 For accessibility, such as with a screen reader
    QAudio::SonificationRole 8 Sonification, such as with user interface sounds
    QAudio::GameRole 9 Game audio
    QAudio::CustomRole 10 The role is specified by QMediaPlayer::customAudioRole()

    This enum was introduced or modified in Qt 5.6.

    See also QMediaPlayer::setAudioRole().

    enum QAudio::State

    Constant Value Description
    QAudio::ActiveState 0 Audio data is being processed, this state is set after start() is called and while audio data is available to be processed.
    QAudio::SuspendedState 1 The audio stream is in a suspended state. Entered after suspend() is called or when another stream takes control of the audio device. In the later case, a call to resume will return control of the audio device to this stream. This should usually only be done upon user request.
    QAudio::StoppedState 2 The audio device is closed, and is not processing any audio data
    QAudio::IdleState 3 The QIODevice passed in has no data and audio system's buffer is empty, this state is set after start() is called and while no audio data is available to be processed.
    QAudio::InterruptedState 4 This stream is in a suspended state because another higher priority stream currently has control of the audio device. Playback cannot resume until the higher priority stream relinquishes control of the audio device.

    enum QAudio::VolumeScale

    This enum defines the different audio volume scales.

    Constant Value Description
    QAudio::LinearVolumeScale 0 Linear scale. 0.0 (0%) is silence and 1.0 (100%) is full volume. All Qt Multimedia classes that have an audio volume use a linear scale.
    QAudio::CubicVolumeScale 1 Cubic scale. 0.0 (0%) is silence and 1.0 (100%) is full volume.
    QAudio::LogarithmicVolumeScale 2 Logarithmic Scale. 0.0 (0%) is silence and 1.0 (100%) is full volume. UI volume controls should usually use a logarithmic scale.
    QAudio::DecibelVolumeScale 3 Decibel (dB, amplitude) logarithmic scale. -200 is silence and 0 is full volume.

    This enum was introduced or modified in Qt 5.8.

    See also QAudio::convertVolume().

    Function Documentation

    qreal QAudio::convertVolume(qreal volume, QAudio::VolumeScale from, QAudio::VolumeScale to)

    Converts an audio volume from a volume scale to another, and returns the result.

    Depending on the context, different scales are used to represent audio volume. All Qt Multimedia classes that have an audio volume use a linear scale, the reason is that the loudness of a speaker is controlled by modulating its voltage on a linear scale. The human ear on the other hand, perceives loudness in a logarithmic way. Using a logarithmic scale for volume controls is therefore appropriate in most applications. The decibel scale is logarithmic by nature and is commonly used to define sound levels, it is usually used for UI volume controls in professional audio applications. The cubic scale is a computationally cheap approximation of a logarithmic scale, it provides more control over lower volume levels.

    The following example shows how to convert the volume value from a slider control before passing it to a QMediaPlayer. As a result, the perceived increase in volume is the same when increasing the volume slider from 20 to 30 as it is from 50 to 60:

    void applyVolume(int volumeSliderValue)
    {
        // volumeSliderValue is in the range [0..100]
    
        qreal linearVolume = QAudio::convertVolume(volumeSliderValue / qreal(100.0),
                                                   QAudio::LogarithmicVolumeScale,
                                                   QAudio::LinearVolumeScale);
    
        player.setVolume(qRound(linearVolume * 100));
    }

    This function was introduced in Qt 5.8.

    See also VolumeScale, QMediaPlayer::setVolume(), QAudioOutput::setVolume(), QAudioInput::setVolume(), QSoundEffect::setVolume(), and QMediaRecorder::setVolume().

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