Qt 5.9 | Qt Multimedia | QAudio Namespace

Qt 5.9.9 Reference Documentation

# 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, ..., GameRole }
enum | State { ActiveState, SuspendedState, StoppedState, IdleState }
enum | VolumeScale { LinearVolumeScale, CubicVolumeScale, LogarithmicVolumeScale, DecibelVolumeScale }

## Functions

qreal | convertVolume(qreal volume, VolumeScale from, 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

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 device is in a suspended state, this state will only be entered after suspend() is called.
`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.

### 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, VolumeScale from, 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().