Audio Overview

For playing media or audio files that are not simple, uncompressed audio, you can use the QMediaPlayer C++ class, or the MediaPlayer QML type. The QMediaPlayer class and associated QML types are also capable of playing video, if required.

See Supported Media Formats for more detail.

The media player needs to be connected to a QAudioOutput object (or the QML AudioOutput element) to play back audio.

Here is how you play a local file using C++:

player = new QMediaPlayer;
audioOutput = new QAudioOutput;
player->setAudioOutput(audioOutput);
// ...
player->setSource(QUrl::fromLocalFile("/Users/me/Music/coolsong.mp3"));
audioOutput->setVolume(50);
player->play();

The same functionality in QML:

MediaPlayer {
    audioOutput: AudioOutput {}
    source: "file:///path/to/my/music.mp3"
    Component.onCompleted: { play() }
}

To record audio to a file, you need to create a capture session and connect to it an audio input and a recorder. These elements are implemented with the QMediaCaptureSession, QAudioInput, and QMediaRecorder classes. The default constructed QAudioInput selects the system default audio input. The recorder controls the recording process with a simple record() and stop() functions. Additionally, you can use it to select the output location, audio encoder, or file container format.

A session recording audio from the default microphone would look as follows in C++:

QMediaCaptureSession session;
QAudioInput audioInput;
session.setAudioInput(&input);
QMediaRecorder recorder;
session.setRecorder(&recorder);
recorder.setQuality(QMediaRecorder::HighQuality);
recorder.setOutputLocation(QUrl::fromLocalFile("test.mp3"));
recorder.record();

In QML, the same can be achieved by:

CaptureSession {
    audioInput: AudioInput {}
    mediaRecorder: MediaRecorder {
        id: recorder
        outputLocation: "file:///path/to/test.mp3"
    }
    Component.onCompleted: { recorder.record() }
}

QMediaCaptureSession also provides support for more complex use cases such as image capturing or video recording.

In addition to raw access to sound devices, the QSoundEffect class (and SoundEffect QML type) offers a more abstract way to play sounds. This class allows you to specify a WAV format file, which can then be played with low latency when necessary.

You can adjust the:

• Number of loops in which a sound effect is played.

• Volume of the sound effect.

• Muting of the sound effect.

The C++ API of Qt Multimedia offers classes for raw access to audio input and output facilities, allowing applications to receive raw data from devices like microphones, and to write raw data to speakers or other devices. Generally these classes do not do any audio decoding, or other processing, but they can support different types of raw audio data.

The QAudioSink class offers raw audio data output, while QAudioSource offers raw audio data input. The available hardware determines what audio outputs and inputs are available.

Push and Pull▲

In some cases you may want to decode a compressed audio file and do further processing yourself. For example, mixing multiple samples or using custom digital signal processing algorithms. QAudioDecoder supports decoding local files or data streams from QIODevice instances.

Here's an example of decoding a local file:

QAudioFormat desiredFormat;
desiredFormat.setChannelCount(2);
desiredFormat.setSampleFormat(QAudioFormat::Int16);
desiredFormat.setSampleRate(48000);

QAudioDecoder *decoder = new QAudioDecoder(this);
decoder->setAudioFormat(desiredFormat);
decoder->setSource("level1.mp3");

connect(decoder, SIGNAL(bufferReady()), this, SLOT(readBuffer()));
decoder->start();

// Now wait for bufferReady() signal and call decoder->read()

The Qt Spatial Audio module provides an API for implementation sound fields in 3D space.

• QAmbientSound: A stereo overlay sound.

• QAudio: The QAudio namespace contains enums used by the audio classes.

• QAudioBuffer: The QAudioBuffer class represents a collection of audio samples with a specific format and sample rate.

• QAudioDecoder: The QAudioDecoder class implements decoding audio.

• QAudioDevice: The QAudioDevice class provides an information about audio devices and their functionality.

• QAudioEngine: QAudioEngine manages a three dimensional sound field.

• QAudioFormat: The QAudioFormat class stores audio stream parameter information.

• QAudioInput: Represents an input channel for audio.

• QAudioListener: Defines the position and orientation of the person listening to a sound field defined by QAudioEngine.

• QAudioOutput: Represents an output channel for audio.

• QAudioRoom:

• QAudioSink: The QAudioSink class provides an interface for sending audio data to an audio output device.

• QAudioSource: The QAudioSource class provides an interface for receiving audio data from an audio input device.

• QMediaCaptureSession: The QMediaCaptureSession class allows capturing of audio and video content.

• QMediaRecorder: The QMediaRecorder class is used for encoding and recording a capture session.

• QSoundEffect: The QSoundEffect class provides a way to play low latency sound effects.

• QSpatialSound: A sound object in 3D space.

• AmbientSound: A stereo overlay sound.

• AudioEngine: AudioEngine manages sound objects inside a 3D scene.

• AudioInput: An audio input to be used for capturing audio in a capture session.

• AudioListener: defines the position and orientation of the person listening to a sound field defined by a AudioEngine.

• AudioOutput: An audio output to be used for playback or monitoring of a capture session.

• AudioRoom:

• CaptureSession: Allows capturing of audio and video content.

• MediaPlayer: Adds media playback to a scene.

• MediaRecorder: For encoding and recording media generated in a CaptureSession.

• SoundEffect: The SoundEffect type provides a way to play sound effects in QML.

• SpatialSound: A sound object in 3D space.

• audioDevice: Describes an audio device.

• mediaMetaData: Provides meta-data for media files.

• Audio Devices Example: Testing the available audio devices and their configuration.

• Audio Output Example: Enabling audio playback using the QAudioSink class.

• Audio Recorder Example: Discovering the available devices and supported codecs.

• Audio Source Example: Recording audio using the QAudioSource class.

• Spatial Audio Panning Example: Shows some of the capabilities of the spatial audio engine in Qt.