Qt 5.11 | Qt Multimedia | C++ Classes | QCamera

Qt 5.11.3 Reference Documentation

# QCamera Class

The QCamera class provides interface for system camera devices. More...

Header: | #include <QCamera>
qmake: | QT += multimedia
Inherits: | QMediaObject

- List of all members, including inherited members
- Obsolete members

## Public Types

class | FrameRateRange
enum | CaptureMode { CaptureViewfinder, CaptureStillImage, CaptureVideo }
flags | CaptureModes
enum | Error { NoError, CameraError, InvalidRequestError, ServiceMissingError, NotSupportedFeatureError }
enum | LockChangeReason { UserRequest, LockAcquired, LockFailed, LockLost, LockTemporaryLost }
enum | LockStatus { Unlocked, Searching, Locked }
enum | LockType { NoLock, LockExposure, LockWhiteBalance, LockFocus }
flags | LockTypes
enum | Position { UnspecifiedPosition, BackFace, FrontFace }
enum | State { UnloadedState, LoadedState, ActiveState }
enum | Status { ActiveStatus, StartingStatus, StoppingStatus, StandbyStatus, ..., UnavailableStatus }

## Properties

- captureMode : QCamera::CaptureModes
- lockStatus : const QCamera::LockStatus
- state : const QCamera::State
- status : const QCamera::Status

- 1 property inherited from QMediaObject

## Public Functions

| QCamera(QObject *parent = nullptr)
| QCamera(const QByteArray &deviceName, QObject *parent = nullptr)
| QCamera(const QCameraInfo &cameraInfo, QObject *parent = nullptr)
| QCamera(QCamera::Position position, QObject *parent = nullptr)
virtual | ~QCamera()
QCamera::CaptureModes | captureMode() const
QCamera::Error | error() const
QString | errorString() const
QCameraExposure * | exposure() const
QCameraFocus * | focus() const
QCameraImageProcessing * | imageProcessing() const
bool | isCaptureModeSupported(QCamera::CaptureModes mode) const
QCamera::LockStatus | lockStatus() const
QCamera::LockStatus | lockStatus(QCamera::LockType lockType) const
QCamera::LockTypes | requestedLocks() const
void | setViewfinder(QVideoWidget *viewfinder)
void | setViewfinder(QGraphicsVideoItem *viewfinder)
void | setViewfinder(QAbstractVideoSurface *surface)
void | setViewfinderSettings(const QCameraViewfinderSettings &settings)
QCamera::State | state() const
QCamera::Status | status() const
QCamera::LockTypes | supportedLocks() const
QList<QCamera::FrameRateRange> | supportedViewfinderFrameRateRanges(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const
QList<QVideoFrame::PixelFormat> | supportedViewfinderPixelFormats(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const
QList<QSize> | supportedViewfinderResolutions(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const
QList<QCameraViewfinderSettings> | supportedViewfinderSettings(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const
QCameraViewfinderSettings | viewfinderSettings() const

## Reimplemented Public Functions

virtual QMultimedia::AvailabilityStatus | availability() const override

- 10 public functions inherited from QMediaObject

## Public Slots

void | load()
void | searchAndLock()
void | searchAndLock(QCamera::LockTypes locks)
void | setCaptureMode(QCamera::CaptureModes mode)
void | start()
void | stop()
void | unload()
void | unlock()
void | unlock(QCamera::LockTypes locks)

## Signals

void | captureModeChanged(QCamera::CaptureModes mode)
void | error(QCamera::Error value)
void | lockFailed()
void | lockStatusChanged(QCamera::LockStatus status, QCamera::LockChangeReason reason)
void | lockStatusChanged(QCamera::LockType lock, QCamera::LockStatus status, QCamera::LockChangeReason reason)
void | locked()
void | stateChanged(QCamera::State state)
void | statusChanged(QCamera::Status status)

- 6 signals inherited from QMediaObject

### Additional Inherited Members

- 2 protected functions inherited from QMediaObject

## Detailed Description

The QCamera class provides interface for system camera devices.

QCamera can be used with QCameraViewfinder for viewfinder display, QMediaRecorder for video recording and QCameraImageCapture for image taking.

You can use QCameraInfo to list available cameras and choose which one to use.

      QList<QCameraInfo> cameras = QCameraInfo::availableCameras();
      foreach (const QCameraInfo &cameraInfo, cameras) {
          if (cameraInfo.deviceName() == "mycamera")
              camera = new QCamera(cameraInfo);
      }

See the camera overview for more information.

## Member Type Documentation

### enum QCamera::CaptureMode
flags QCamera::CaptureModes

Constant | Value | Description
--- | --- | ---
`QCamera::CaptureViewfinder` | `0` | Camera is only configured to display viewfinder.
`QCamera::CaptureStillImage` | `0x01` | Camera is configured for still frames capture.
`QCamera::CaptureVideo` | `0x02` | Camera is configured for video capture.

The CaptureModes type is a typedef for QFlags<CaptureMode>. It stores an OR combination of CaptureMode values.

### enum QCamera::Error

Constant | Value | Description
--- | --- | ---
`QCamera::NoError` | `0` | No errors have occurred.
`QCamera::CameraError` | `1` | An error has occurred.
`QCamera::InvalidRequestError` | `2` | System resource doesn't support requested functionality.
`QCamera::ServiceMissingError` | `3` | No camera service available.
`QCamera::NotSupportedFeatureError` | `4` | The feature is not supported.

### enum QCamera::LockChangeReason

Constant | Value | Description
--- | --- | ---
`QCamera::UserRequest` | `0` | The lock status changed in result of user request, usually to unlock camera settings.
`QCamera::LockAcquired` | `1` | The lock status successfuly changed to QCamera::Locked.
`QCamera::LockFailed` | `2` | The camera failed to acquire the requested lock in result of autofocus failure, exposure out of supported range, etc.
`QCamera::LockLost` | `3` | The camera is not able to maintain the requested lock any more. Lock status is changed to QCamera::Unlocked.
`QCamera::LockTemporaryLost` | `4` | The lock is lost, but the camera is working hard to reacquire it. This value may be used in continuous focusing mode, when the camera loses the focus, the focus lock state is changed to Qcamera::Searching with LockTemporaryLost reason.

### enum QCamera::LockStatus

Constant | Value | Description
--- | --- | ---
`QCamera::Unlocked` | `0` | The application is not interested in camera settings value. The camera may keep this parameter without changes, this is common with camera focus, or adjust exposure and white balance constantly to keep the viewfinder image nice.
`QCamera::Searching` | `1` | The application has requested the camera focus, exposure or white balance lock with QCamera::searchAndLock(). This state indicates the camera is focusing or calculating exposure and white balance.
`QCamera::Locked` | `2` | The camera focus, exposure or white balance is locked. The camera is ready to capture, application may check the exposure parameters.

The locked state usually means the requested parameter stays the same, except of the cases when the parameter is requested to be constantly updated. For example in continuous focusing mode, the focus is considered locked as long and the object is in focus, even while the actual focusing distance may be constantly changing.

### enum QCamera::LockType
flags QCamera::LockTypes

Constant | Value | Description
--- | --- | ---
`QCamera::NoLock` | `0` |
`QCamera::LockExposure` | `0x01` | Lock camera exposure.
`QCamera::LockWhiteBalance` | `0x02` | Lock the white balance.
`QCamera::LockFocus` | `0x04` | Lock camera focus.

The LockTypes type is a typedef for QFlags<LockType>. It stores an OR combination of LockType values.

### enum QCamera::Position

This enum specifies the physical position of the camera on the system hardware.

Constant | Value | Description
--- | --- | ---
`QCamera::UnspecifiedPosition` | `0` | The camera position is unspecified or unknown.
`QCamera::BackFace` | `1` | The camera is on the back face of the system hardware. For example on a mobile device, it means it is on the opposite side to that of the screen.
`QCamera::FrontFace` | `2` | The camera is on the front face of the system hardware. For example on a mobile device, it means it is on the same side as that of the screen. Viewfinder frames of front-facing cameras are mirrored horizontally, so the users can see themselves as looking into a mirror. Captured images or videos are not mirrored.

This enum was introduced or modified in Qt 5.3.

See also QCameraInfo::position().

### enum QCamera::State

Constant | Value | Description
--- | --- | ---
`QCamera::UnloadedState` | `0` | The initial camera state, with camera not loaded, the camera capabilities except of supported capture modes are unknown.

While the supported settings are unknown in this state, it's allowed to set the camera capture settings like codec, resolution, or frame rate.

Constant | Value | Description
--- | --- | ---
`QCamera::LoadedState` | `1` | The camera is loaded and ready to be configured.

In the Idle state it's allowed to query camera capabilities, set capture resolution, codecs, etc.

The viewfinder is not active in the loaded state.

Constant | Value | Description
--- | --- | ---
`QCamera::ActiveState` | `2` | In the active state as soon as camera is started the viewfinder displays video frames and the camera is ready for capture.

### enum QCamera::Status

Constant | Value | Description
--- | --- | ---
`QCamera::ActiveStatus` | `8` | The camera has been started and can produce data. The viewfinder displays video frames in active state.

Depending on backend, changing some camera settings like capture mode, codecs or resolution in ActiveState may lead to changing the camera status to LoadedStatus and StartingStatus while the settings are applied and back to ActiveStatus when the camera is ready.

Constant | Value | Description
--- | --- | ---
`QCamera::StartingStatus` | `6` | The camera is starting in result of state transition to QCamera::ActiveState. The camera service is not ready to capture yet.
`QCamera::StoppingStatus` | `7` | The camera is stopping in result of state transition from QCamera::ActiveState to QCamera::LoadedState or QCamera::UnloadedState.
`QCamera::StandbyStatus` | `5` | The camera is in the power saving standby mode. The camera may come to the standby mode after some time of inactivity in the QCamera::LoadedState state.
`QCamera::LoadedStatus` | `4` | The camera is loaded and ready to be configured. This status indicates the camera device is opened and it's possible to query for supported image and video capture settings, like resolution, framerate and codecs.
`QCamera::LoadingStatus` | `2` | The camera device loading in result of state transition from QCamera::UnloadedState to QCamera::LoadedState or QCamera::ActiveState.
`QCamera::UnloadingStatus` | `3` | The camera device is unloading in result of state transition from QCamera::LoadedState or QCamera::ActiveState to QCamera::UnloadedState.
`QCamera::UnloadedStatus` | `1` | The initial camera status, with camera not loaded. The camera capabilities including supported capture settings may be unknown.
`QCamera::UnavailableStatus` | `0` | The camera or camera backend is not available.

## Property Documentation

### captureMode : QCamera::CaptureModes

The type of media (video or still images), the camera is configured to capture.

It's allowed to change capture mode in any camera state, but if the camera is currently active, chaging capture mode is likely to lead to camera status chaged to QCamera::LoadedStatus, QCamera::LoadingStatus, and when the camera is ready to QCamera::ActiveStatus.

Access functions:

QCamera::CaptureModes | captureMode() const
void | setCaptureMode(QCamera::CaptureModes mode)

Notifier signal:

void | captureModeChanged(QCamera::CaptureModes mode)

### lockStatus : const QCamera::LockStatus

This property holds the overall status for all the requested camera locks.

Access functions:

QCamera::LockStatus | lockStatus() const
QCamera::LockStatus | lockStatus(QCamera::LockType lockType) const

Notifier signal:

void | lockStatusChanged(QCamera::LockStatus status, QCamera::LockChangeReason reason)
void | lockStatusChanged(QCamera::LockType lock, QCamera::LockStatus status, QCamera::LockChangeReason reason)

### state : const QCamera::State

This property holds the current state of the camera object.

Access functions:

QCamera::State | state() const

Notifier signal:

void | stateChanged(QCamera::State state)

### status : const QCamera::Status

This property holds the current status of the camera object.

Access functions:

QCamera::Status | status() const

Notifier signal:

void | statusChanged(QCamera::Status status)

## Member Function Documentation

### QCamera::QCamera(QObject *parent = nullptr)

Construct a QCamera with a parent.

### QCamera::QCamera(const QByteArray &deviceName, QObject *parent = nullptr)

Construct a QCamera from deviceName and parent.

If no camera with that deviceName exists, the camera object will be invalid.

### QCamera::QCamera(const QCameraInfo &cameraInfo, QObject *parent = nullptr)

Construct a QCamera from a camera description cameraInfo and parent.

This function was introduced in Qt 5.3.

### QCamera::QCamera(QCamera::Position position, QObject *parent = nullptr)

Construct a QCamera which uses a hardware camera located a the specified position.

For example on a mobile phone it can be used to easily choose between front-facing and back-facing cameras.

If no camera is available at the specified position or if position is QCamera::UnspecifiedPosition, the default camera is used.

This function was introduced in Qt 5.3.

### `[virtual]` QCamera::~QCamera()

Destroys the camera object.

### `[override virtual]` QMultimedia::AvailabilityStatus QCamera::availability() const

Reimplemented from QMediaObject::availability().

Returns the availability state of the camera service.

### `[signal]` void QCamera::captureModeChanged(QCamera::CaptureModes mode)

Signals the capture mode has changed.

Note: Notifier signal for property captureMode.

### QCamera::Error QCamera::error() const

Returns the error state of the object.

### `[signal]` void QCamera::error(QCamera::Error value)

Signal emitted when error state changes to value.

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(camera, QOverload<QCamera::Error>::of(&QCamera::error),
          [=](QCamera::Error value){ /* ... */ });

### QString QCamera::errorString() const

Returns a string describing a camera's error state.

### QCameraExposure *QCamera::exposure() const

Returns the camera exposure control object.

### QCameraFocus *QCamera::focus() const

Returns the camera focus control object.

### QCameraImageProcessing *QCamera::imageProcessing() const

Returns the camera image processing control object.

### bool QCamera::isCaptureModeSupported(QCamera::CaptureModes mode) const

Returns true if the capture mode is suported.

### `[slot]` void QCamera::load()

Open the camera device. The camera state is changed to QCamera::LoadedStatus.

It's not necessary to explcitly load the camera, unless unless the application have to read the supported camera settings and change the default depending on the camera capabilities.

In all the other cases it's possible to start the camera directly from unloaded state.

### `[signal]` void QCamera::lockFailed()

Signals locking of at least one requested camera settings failed.

### QCamera::LockStatus QCamera::lockStatus() const

Returns the status of requested camera settings locks.

Note: Getter function for property lockStatus.

### QCamera::LockStatus QCamera::lockStatus(QCamera::LockType lockType) const

Returns the lock status for a given lockType.

Note: Getter function for property lockStatus.

### `[signal]` void QCamera::lockStatusChanged(QCamera::LockStatus status, QCamera::LockChangeReason reason)

Signals the overall status for all the requested camera locks was changed with specified reason.

Note: Signal lockStatusChanged 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(camera, QOverload<QCamera::LockStatus, QCamera::LockChangeReason>::of(&QCamera::lockStatusChanged),
          [=](QCamera::LockStatus status, QCamera::LockChangeReason reason){ /* ... */ });

Note: Notifier signal for property lockStatus.

### `[signal]` void QCamera::lockStatusChanged(QCamera::LockType lock, QCamera::LockStatus status, QCamera::LockChangeReason reason)

Signals the lock status was changed with specified reason.

Note: Signal lockStatusChanged 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(camera, QOverload<QCamera::LockType, QCamera::LockStatus, QCamera::LockChangeReason>::of(&QCamera::lockStatusChanged),
          [=](QCamera::LockType lock, QCamera::LockStatus status, QCamera::LockChangeReason reason){ /* ... */ });

Note: Notifier signal for property lockStatus.

### `[signal]` void QCamera::locked()

Signals all the requested camera settings are locked.

### QCamera::LockTypes QCamera::requestedLocks() const

Returns the requested lock types.

### `[slot]` void QCamera::searchAndLock()

Lock all the supported camera settings.

### `[slot]` void QCamera::searchAndLock(QCamera::LockTypes locks)

Locks the camera settings with the requested locks, including focusing in the single autofocus mode, exposure and white balance if the exposure and white balance modes are not manual.

The camera settings are usually locked before taking one or multiple still images, in responce to the shutter button being half pressed.

The QCamera::locked() signal is emitted when camera settings are successfully locked, otherwise QCamera::lockFailed() is emitted.

QCamera also emits lockStatusChanged(QCamera::LockType, QCamera::LockStatus) on individual lock status changes and lockStatusChanged(QCamera::LockStatus) signal on composite status changes.

Locking serves two roles: it initializes calculation of automatic parameter (focusing, calculating the correct exposure and white balance) and allows to keep some or all of those parameters during number of shots.

If the camera doesn't support keeping one of parameters between shots, the related lock state changes to QCamera::Unlocked.

It's also acceptable to relock already locked settings, depending on the lock parameter this initiates new focusing, exposure or white balance calculation.

### void QCamera::setViewfinder(QVideoWidget *viewfinder)

Sets the QVideoWidget based camera viewfinder. The previously set viewfinder is detached.

### void QCamera::setViewfinder(QGraphicsVideoItem *viewfinder)

Sets the QGraphicsVideoItem based camera viewfinder. The previously set viewfinder is detached.

### void QCamera::setViewfinder(QAbstractVideoSurface *surface)

Sets a video surface as the viewfinder of a camera.

If a viewfinder has already been set on the camera the new surface will replace it.

### void QCamera::setViewfinderSettings(const QCameraViewfinderSettings &settings)

Sets the viewfinder settings.

If some parameters are not specified, or null settings are passed, the camera will choose default values.

If the camera is used to capture videos or images, the viewfinder settings might be ignored if they conflict with the capture settings. You can check the actual viewfinder settings once the camera is in the `QCamera::ActiveStatus` status.

Changing the viewfinder settings while the camera is in the QCamera::ActiveState state may cause the camera to be restarted.

This function was introduced in Qt 5.5.

See also viewfinderSettings(), supportedViewfinderResolutions(), supportedViewfinderFrameRateRanges(), and supportedViewfinderPixelFormats().

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

Starts the camera.

State is changed to QCamera::ActiveState if camera is started successfully, otherwise error() signal is emitted.

While the camera state is changed to QCamera::ActiveState, starting the camera service can be asynchronous with the actual status reported with QCamera::status property.

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

Signals the camera state has changed.

Usually the state changes is caused by calling load(), unload(), start() and stop(), but the state can also be changed change as a result of camera error.

Note: Notifier signal for property state.

### `[signal]` void QCamera::statusChanged(QCamera::Status status)

Signals the camera status has changed.

Note: Notifier signal for property status.

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

Stops the camera. The camera state is changed from QCamera::ActiveState to QCamera::LoadedState.

### QCamera::LockTypes QCamera::supportedLocks() const

Returns the lock types, camera supports.

### QList<QCamera::FrameRateRange> QCamera::supportedViewfinderFrameRateRanges(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const

Returns a list of supported viewfinder frame rate ranges.

This is a convenience function which retrieves unique frame rate ranges from the supported settings.

If non null viewfinder settings are passed, the returned list is reduced to frame rate ranges supported with partial settings applied.

The camera must be loaded before calling this function, otherwise the returned list is empty.

This function was introduced in Qt 5.5.

See also QCameraViewfinderSettings::minimumFrameRate(), QCameraViewfinderSettings::maximumFrameRate(), and setViewfinderSettings().

### QList<QVideoFrame::PixelFormat> QCamera::supportedViewfinderPixelFormats(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const

Returns a list of supported viewfinder pixel formats.

This is a convenience function which retrieves unique pixel formats from the supported settings.

If non null viewfinder settings are passed, the returned list is reduced to pixel formats supported with partial settings applied.

The camera must be loaded before calling this function, otherwise the returned list is empty.

This function was introduced in Qt 5.5.

See also QCameraViewfinderSettings::pixelFormat() and setViewfinderSettings().

### QList<QSize> QCamera::supportedViewfinderResolutions(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const

Returns a list of supported viewfinder resolutions.

This is a convenience function which retrieves unique resolutions from the supported settings.

If non null viewfinder settings are passed, the returned list is reduced to resolutions supported with partial settings applied.

The camera must be loaded before calling this function, otherwise the returned list is empty.

This function was introduced in Qt 5.5.

See also QCameraViewfinderSettings::resolution() and setViewfinderSettings().

### QList<QCameraViewfinderSettings> QCamera::supportedViewfinderSettings(const QCameraViewfinderSettings &settings = QCameraViewfinderSettings()) const

Returns a list of supported viewfinder settings.

The list is ordered by preference; preferred settings come first.

The optional settings argument can be used to conveniently filter the results. If settings is non null, the returned list is reduced to settings matching the given partial settings.

The camera must be loaded before calling this function, otherwise the returned list is empty.

This function was introduced in Qt 5.5.

See also setViewfinderSettings(), supportedViewfinderResolutions(), supportedViewfinderFrameRateRanges(), and supportedViewfinderPixelFormats().

### `[slot]` void QCamera::unload()

Close the camera device and deallocate the related resources. The camera state is changed to QCamera::UnloadedStatus.

### `[slot]` void QCamera::unlock()

Unlock all the requested camera locks.

### `[slot]` void QCamera::unlock(QCamera::LockTypes locks)

Unlocks the camera settings specified with locks or cancel the current locking if one is active.

### QCameraViewfinderSettings QCamera::viewfinderSettings() const

Returns the viewfinder settings being used by the camera.

Settings may change when the camera is started, for example if the viewfinder settings are undefined or if unsupported values are set.

If viewfinder settings are not supported by the camera, it always returns a null QCameraViewfinderSettings object.

This function was introduced in Qt 5.5.

See also setViewfinderSettings().