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

struct	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, LoadedStatus, …, UnavailableStatus }

Properties

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

Public Functions

	QCamera(QCamera::Position position, QObject *parent = nullptr)
	QCamera(const QCameraInfo &cameraInfo, QObject *parent = nullptr)
	QCamera(const QByteArray &deviceName, QObject *parent = nullptr)
	QCamera(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

Public Slots

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

Signals

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

Detailed Description

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.

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

See the camera overview for more information.

Member Type Documentation

enum QCamera::CaptureModeflags QCamera::CaptureModes

This enum holds the capture mode of the camera.

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

This enum holds the last error code.

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

This enum holds the reason why the camera lock status changed.

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

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

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

enum QCamera::LockTypeflags QCamera::LockTypes

This enum holds the camera lock type.

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

This enum holds the current state of the camera.

Constant	Value	Description
QCamera::UnloadedState	0	The initial camera state, with camera not loaded. The camera capabilities, except 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.
QCamera::LoadedState	1	The camera is loaded and ready to be configured. In this state it's allowed to query camera capabilities, set capture resolution, codecs, etc. The viewfinder is not active in the loaded state. The camera consumes power in the loaded state.
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

This enum holds the current status of the camera.

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.
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.

Member Function Documentation

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.

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(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(QObject *parent = nullptr)

Construct a QCamera with a parent.

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

Signals the capture mode has changed.

Note: Notifier signal for property captureMode.

[signal] void QCamera::errorOccurred(QCamera::Error value)

Signal emitted when error state changes to value.

This function was introduced in Qt 5.15.

[slot] void QCamera::load()

Opens the camera device. The camera state is changed to QCamera::LoadedState.

It's not necessary to explicitly load the camera, unless the application needs to read the supported camera settings and change the default values according to the camera capabilities.

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

/sa QCamera::UnloadedState

[signal] void QCamera::lockFailed()

Signals locking of at least one requested camera settings failed.

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

Signals the lock status was changed with specified reason.

Note: Notifier signal for property lockStatus.

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){ /* ... */ });

[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: Notifier signal for property lockStatus.

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){ /* ... */ });

[signal] void QCamera::locked()

Signals all the requested camera settings are locked.

[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.

[slot] void QCamera::searchAndLock()

Lock all the supported camera settings.

[slot] void QCamera::start()

Starts the camera.

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

In this state, the camera still consumes power.

See also unload() and QCamera::UnloadedState.

[slot] void QCamera::unload()

Closes the camera device and deallocates the related resources. The camera state is changed to QCamera::UnloadedState.

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

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

[slot] void QCamera::unlock()

Unlock all the requested camera locks.

[virtual] QCamera::~QCamera()

Destroys the camera object.

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

Reimplements: QMediaObject::availability() const.

Returns the availability state of the camera service.

QCamera::Error QCamera::error() const

Returns the error state of the object.

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.

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.

QCamera::LockTypes QCamera::requestedLocks() const

Returns the requested lock types.

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().

QCamera::LockTypes QCamera::supportedLocks() const

Returns the lock types that the 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 status of the camera must be LoadedStatus 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().

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().