- Qt 6.9
- Qt Multimedia
- C++ Classes
- QtMultimedia
- QAudioDecoder
- Qt 6.9.2 Reference Documentation

# QAudioDecoder Class

The QAudioDecoder class implements decoding audio. More...

Header: | `#include <QAudioDecoder>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Multimedia)` `target_link_libraries(mytarget PRIVATE Qt6::Multimedia)`
qmake: | `QT += multimedia`
Inherits: | QObject
Status: | Preliminary

This class is under development and is subject to change.

- List of all members, including inherited members

## Public Types

enum | Error { NoError, ResourceError, FormatError, AccessDeniedError, NotSupportedError }

## Properties

- bufferAvailable : const bool
- error : const QString
- isDecoding : const bool
- source : QUrl

## Public Functions

| QAudioDecoder(QObject *parent = nullptr)
virtual | ~QAudioDecoder() override
QAudioFormat | audioFormat() const
bool | bufferAvailable() const
qint64 | duration() const
QAudioDecoder::Error | error() const
QString | errorString() const
bool | isDecoding() const
bool | isSupported() const
qint64 | position() const
QAudioBuffer | read() const
void | setAudioFormat(const QAudioFormat &format)
void | setSource(const QUrl &fileName)
void | setSourceDevice(QIODevice *device)
QUrl | source() const
QIODevice * | sourceDevice() const

## Public Slots

void | start()
void | stop()

## Signals

void | bufferAvailableChanged(bool available)
void | bufferReady()
void | durationChanged(qint64 duration)
void | error(QAudioDecoder::Error error)
void | finished()
void | formatChanged(const QAudioFormat &format)
void | isDecodingChanged(bool)
void | positionChanged(qint64 position)
void | sourceChanged()

## Detailed Description

The QAudioDecoder class is a high level class for decoding audio media files. It is similar to the QMediaPlayer class except that audio is provided back through this API rather than routed directly to audio hardware.

See also QAudioBuffer.

## Member Type Documentation

### enum QAudioDecoder::Error

Defines a media player error condition.

Constant | Value | Description
--- | --- | ---
`QAudioDecoder::NoError` | `0` | No error has occurred.
`QAudioDecoder::ResourceError` | `1` | A media resource couldn't be resolved.
`QAudioDecoder::FormatError` | `2` | The format of a media resource isn't supported.
`QAudioDecoder::AccessDeniedError` | `3` | There are not the appropriate permissions to play a media resource.
`QAudioDecoder::NotSupportedError` | `4` | QAudioDecoder is not supported on this platform

## Property Documentation

### `[read-only]` bufferAvailable : const bool

This property holds whether there is a decoded audio buffer available

Access functions:

bool | bufferAvailable() const

Notifier signal:

void | bufferAvailableChanged(bool available)

### `[read-only]` error : const QString

Returns a human readable description of the current error, or an empty string is there is no error.

Access functions:

QString | errorString() const

### `[read-only]` isDecoding : const bool

`true` if the decoder is currently running and decoding audio data.

Access functions:

bool | isDecoding() const

Notifier signal:

void | isDecodingChanged(bool)

### source : QUrl

This property holds the active filename being decoded by the decoder object.

Access functions:

QUrl | source() const
void | setSource(const QUrl &fileName)

Notifier signal:

void | sourceChanged()

## Member Function Documentation

### `[explicit]` QAudioDecoder::QAudioDecoder(QObject *parent = nullptr)

Construct an QAudioDecoder instance with parent.

### `[override virtual noexcept]` QAudioDecoder::~QAudioDecoder()

Destroys the audio decoder object.

### QAudioFormat QAudioDecoder::audioFormat() const

Returns the audio format the decoder is set to.

Note: This may be different than the format of the decoded samples, if the audio format was set to an invalid one.

See also setAudioFormat() and formatChanged().

### bool QAudioDecoder::bufferAvailable() const

Returns true if a buffer is available to be read, and false otherwise. If there is no buffer available, calling the read() function will return an invalid buffer.

Note: Getter function for property bufferAvailable.

### `[signal]` void QAudioDecoder::bufferAvailableChanged(bool available)

Signals the availability (if available is true) of a new buffer.

If available is false, there are no buffers available.

Note: Notifier signal for property bufferAvailable.

See also bufferAvailable() and bufferReady().

### `[signal]` void QAudioDecoder::bufferReady()

Signals that a new decoded audio buffer is available to be read.

See also read() and bufferAvailable().

### qint64 QAudioDecoder::duration() const

Returns total duration (in milliseconds) of the audio stream or -1 if not available.

### `[signal]` void QAudioDecoder::durationChanged(qint64 duration)

Signals that the estimated duration of the decoded data has changed.

See also positionChanged().

### QAudioDecoder::Error QAudioDecoder::error() const

Returns the current error state of the QAudioDecoder.

### `[signal]` void QAudioDecoder::error(QAudioDecoder::Error error)

Signals that an error condition has occurred.

Note: Signal error is overloaded in this class. To connect to this signal by using the function pointer syntax, Qt provides a convenient helper for obtaining the function pointer as shown in this example:

     connect(audioDecoder, QOverload<QAudioDecoder::Error>::of(&QAudioDecoder::error),
         [=](QAudioDecoder::Error error){ /* ... */ });

See also errorString().

### `[signal]` void QAudioDecoder::finished()

Signals that the decoding has finished successfully. If decoding fails, error signal is emitted instead.

See also start(), stop(), and error().

### `[signal]` void QAudioDecoder::formatChanged(const QAudioFormat &format)

Signals that the current audio format of the decoder has changed to format.

See also audioFormat() and setAudioFormat().

### bool QAudioDecoder::isSupported() const

Returns true is audio decoding is supported on this platform.

### qint64 QAudioDecoder::position() const

Returns position (in milliseconds) of the last buffer read from the decoder or -1 if no buffers have been read.

### `[signal]` void QAudioDecoder::positionChanged(qint64 position)

Signals that the current position of the decoder has changed.

See also durationChanged().

### QAudioBuffer QAudioDecoder::read() const

Read a buffer from the decoder, if one is available. Returns an invalid buffer if there are no decoded buffers currently available, or on failure. In both cases this function will not block.

You should either respond to the bufferReady() signal or check the bufferAvailable() function before calling read() to make sure you get useful data.

### void QAudioDecoder::setAudioFormat(const QAudioFormat &format)

Set the desired audio format for decoded samples to format.

This property can only be set while the decoder is stopped. Setting this property at other times will be ignored.

If the decoder does not support this format, error() will be set to `FormatError`.

If you do not specify a format, the format of the decoded audio itself will be used. Otherwise, some format conversion will be applied.

If you wish to reset the decoded format to that of the original audio file, you can specify an invalid format.

Warning: Setting a desired audio format is not yet supported on the Android backend. It does work with the default FFMPEG backend.

See also audioFormat().

### void QAudioDecoder::setSource(const QUrl &fileName)

Sets the current audio file name to fileName.

When this property is set any current decoding is stopped, and any audio buffers are discarded.

You can only specify either a source filename or a source QIODevice. Setting one will unset the other.

Note: Setter function for property source.

See also source().

### void QAudioDecoder::setSourceDevice(QIODevice *device)

Sets the current audio QIODevice to device.

When this property is set any current decoding is stopped, and any audio buffers are discarded.

You can only specify either a source filename or a source QIODevice. Setting one will unset the other.

See also sourceDevice().

### QUrl QAudioDecoder::source() const

Returns the current file name to decode. If setSourceDevice was called, this will be empty.

Note: Getter function for property source.

See also setSource().

### `[signal]` void QAudioDecoder::sourceChanged()

Signals that the current source of the decoder has changed.

Note: Notifier signal for property source.

See also source() and sourceDevice().

### QIODevice *QAudioDecoder::sourceDevice() const

Returns the current source QIODevice, if one was set. If setSource() was called, this will be a nullptr.

See also setSourceDevice().

### `[slot]` void QAudioDecoder::start()

Starts decoding the audio resource.

As data gets decoded, the bufferReady() signal will be emitted when enough data has been decoded. Calling read() will then return an audio buffer without blocking.

If you call read() before a buffer is ready, an invalid buffer will be returned, again without blocking.

See also read().

### `[slot]` void QAudioDecoder::stop()

Stop decoding audio. Calling start() again will resume decoding from the beginning.