Qt 5.9 | Qt Multimedia | C++ Classes | QAudioInput

Qt 5.9.4 Reference Documentation

# QAudioInput Class

The QAudioInput class provides an interface for receiving audio data from an audio input device. More...

Header: | #include <QAudioInput>
qmake: | QT += multimedia

- List of all members, including inherited members

## Public Functions

| QAudioInput(const QAudioFormat &format = QAudioFormat(), QObject *parent = Q_NULLPTR)
| QAudioInput(const QAudioDeviceInfo &audioDevice, const QAudioFormat &format = QAudioFormat(), QObject *parent = Q_NULLPTR)
| ~QAudioInput()
int | bufferSize() const
int | bytesReady() const
qint64 | elapsedUSecs() const
QAudio::Error | error() const
QAudioFormat | format() const
int | notifyInterval() const
int | periodSize() const
qint64 | processedUSecs() const
void | reset()
void | resume()
void | setBufferSize(int value)
void | setNotifyInterval(int ms)
void | setVolume(qreal volume)
void | start(QIODevice *device)
QIODevice * | start()
QAudio::State | state() const
void | stop()
void | suspend()
qreal | volume() const

## Signals

void | notify()
void | stateChanged(QAudio::State state)

## Detailed Description

The QAudioInput class provides an interface for receiving audio data from an audio input device.

You can construct an audio input with the system's default audio input device. It is also possible to create QAudioInput with a specific QAudioDeviceInfo. When you create the audio input, you should also send in the QAudioFormat to be used for the recording (see the QAudioFormat class description for details).

To record to a file:

QAudioInput lets you record audio with an audio input device. The default constructor of this class will use the systems default audio device, but you can also specify a QAudioDeviceInfo for a specific device. You also need to pass in the QAudioFormat in which you wish to record.

Starting up the QAudioInput is simply a matter of calling start() with a QIODevice opened for writing. For instance, to record to a file, you can:

      QFile destinationFile;   // Class member
      QAudioInput* audio; // Class member
      {
          destinationFile.setFileName("/tmp/test.raw");
          destinationFile.open( QIODevice::WriteOnly | QIODevice::Truncate );

          QAudioFormat format;
          // Set up the desired format, for example:
          format.setSampleRate(8000);
          format.setChannelCount(1);
          format.setSampleSize(8);
          format.setCodec("audio/pcm");
          format.setByteOrder(QAudioFormat::LittleEndian);
          format.setSampleType(QAudioFormat::UnSignedInt);

          QAudioDeviceInfo info = QAudioDeviceInfo::defaultInputDevice();
          if (!info.isFormatSupported(format)) {
              qWarning() << "Default format not supported, trying to use the nearest.";
              format = info.nearestFormat(format);
          }

          audio = new QAudioInput(format, this);
          connect(audio, SIGNAL(stateChanged(QAudio::State)), this, SLOT(handleStateChanged(QAudio::State)));

          QTimer::singleShot(3000, this, SLOT(stopRecording()));
          audio->start(&destinationFile);
          // Records audio for 3000ms
      }

This will start recording if the format specified is supported by the input device (you can check this with QAudioDeviceInfo::isFormatSupported(). In case there are any snags, use the error() function to check what went wrong. We stop recording in the `stopRecording()` slot.

      void AudioInputExample::stopRecording()
      {
          audio->stop();
          destinationFile.close();
          delete audio;
      }

At any point in time, QAudioInput will be in one of four states: active, suspended, stopped, or idle. These states are specified by the QAudio::State enum. You can request a state change directly through suspend(), resume(), stop(), reset(), and start(). The current state is reported by state(). QAudioOutput will also signal you when the state changes (stateChanged()).

QAudioInput provides several ways of measuring the time that has passed since the start() of the recording. The `processedUSecs()` function returns the length of the stream in microseconds written, i.e., it leaves out the times the audio input was suspended or idle. The elapsedUSecs() function returns the time elapsed since start() was called regardless of which states the QAudioInput has been in.

If an error should occur, you can fetch its reason with error(). The possible error reasons are described by the QAudio::Error enum. The QAudioInput will enter the StoppedState when an error is encountered. Connect to the stateChanged() signal to handle the error:

      void AudioInputExample::handleStateChanged(QAudio::State newState)
      {
          switch (newState) {
              case QAudio::StoppedState:
                  if (audio->error() != QAudio::NoError) {
                      // Error handling
                  } else {
                      // Finished recording
                  }
                  break;

              case QAudio::ActiveState:
                  // Started recording - read from IO device
                  break;

              default:
                  // ... other cases as appropriate
                  break;
          }
      }

See also QAudioOutput and QAudioDeviceInfo.

## Member Function Documentation

### QAudioInput::QAudioInput(const QAudioFormat &format = QAudioFormat(), QObject *parent = Q_NULLPTR)

Construct a new audio input and attach it to parent. The default audio input device is used with the output format parameters.

### QAudioInput::QAudioInput(const QAudioDeviceInfo &audioDevice, const QAudioFormat &format = QAudioFormat(), QObject *parent = Q_NULLPTR)

Construct a new audio input and attach it to parent. The device referenced by audioDevice is used with the input format parameters.

### QAudioInput::~QAudioInput()

Destroy this audio input.

### int QAudioInput::bufferSize() const

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 setBufferSize().

### int QAudioInput::bytesReady() const

Returns the amount of audio data available to read in bytes.

Note: returned value is only valid while in QAudio::ActiveState or QAudio::IdleState state, otherwise returns zero.

### qint64 QAudioInput::elapsedUSecs() const

Returns the microseconds since start() was called, including time in Idle and Suspend states.

### QAudio::Error QAudioInput::error() const

Returns the error state.

### QAudioFormat QAudioInput::format() const

Returns the QAudioFormat being used.

### `[signal]` void QAudioInput::notify()

This signal is emitted when x ms of audio data has been processed the interval set by setNotifyInterval(x).

### int QAudioInput::notifyInterval() const

Returns the notify interval in milliseconds.

See also setNotifyInterval().

### int QAudioInput::periodSize() const

Returns the period size in bytes.

Note: This is the recommended read size in bytes.

### qint64 QAudioInput::processedUSecs() const

Returns the amount of audio data processed since start() was called in microseconds.

### void QAudioInput::reset()

Drops all audio data in the buffers, resets buffers to zero.

### void QAudioInput::resume()

Resumes processing audio data after a suspend().

Sets error() to QAudio::NoError. Sets state() to QAudio::ActiveState if you previously called start(QIODevice*). Sets state() to QAudio::IdleState if you previously called start(). emits stateChanged() signal.

### void QAudioInput::setBufferSize(int value)

Sets the audio buffer size to value 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, calling bufferSize() anytime after start() will return the actual buffer size being used.

See also bufferSize().

### void QAudioInput::setNotifyInterval(int ms)

Sets the interval for notify() signal to be emitted. This is based on the ms of audio data processed not on actual real-time. The minimum resolution of the timer is platform specific and values should be checked with notifyInterval() to confirm actual value being used.

See also notifyInterval().

### void QAudioInput::setVolume(qreal volume)

Sets the input volume to volume.

The volume is scaled linearly from `0.0` (silence) to `1.0` (full volume). Values outside this range will be clamped.

If the device does not support adjusting the input volume then volume will be ignored and the input volume will remain at 1.0.

The default volume is `1.0`.

Note: Adjustments to the volume will change the volume of this audio stream, not the global volume.

See also volume().

### void QAudioInput::start(QIODevice *device)

Starts transferring audio data from the system's audio input to the device. The device must have been opened in the WriteOnly, Append or ReadWrite modes.

If the QAudioInput is able to successfully get audio data, state() returns either QAudio::ActiveState or QAudio::IdleState, error() returns QAudio::NoError and the stateChanged() signal is emitted.

If a problem occurs during this process, error() returns QAudio::OpenError, state() returns QAudio::StoppedState and the stateChanged() signal is emitted.

See also QIODevice.

### QIODevice *QAudioInput::start()

Returns a pointer to the internal QIODevice being used to transfer data from the system's audio input. The device will already be open and read() can read data directly from it.

Note: The pointer will become invalid after the stream is stopped or if you start another stream.

If the QAudioInput is able to access the system's audio device, state() returns QAudio::IdleState, error() returns QAudio::NoError and the stateChanged() signal is emitted.

If a problem occurs during this process, error() returns QAudio::OpenError, state() returns QAudio::StoppedState and the stateChanged() signal is emitted.

See also QIODevice.

### QAudio::State QAudioInput::state() const

Returns the state of audio processing.

### `[signal]` void QAudioInput::stateChanged(QAudio::State state)

This signal is emitted when the device state has changed.

### void QAudioInput::stop()

Stops the audio input, detaching from the system resource.

Sets error() to QAudio::NoError, state() to QAudio::StoppedState and emit stateChanged() signal.

### void QAudioInput::suspend()

Stops processing audio data, preserving buffered audio data.

Sets error() to QAudio::NoError, state() to QAudio::SuspendedState and emit stateChanged() signal.

### qreal QAudioInput::volume() const

Returns the input volume.

If the device does not support adjusting the input volume the returned value will be 1.0.

See also setVolume().