QCamera Class

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

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

Public Types

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 }


Public Functions

QCamera(QObject * parent = 0)
QCamera(const QByteArray & deviceName, QObject * parent = 0)
QCamera(const QCameraInfo & cameraInfo, QObject * parent = 0)
QCamera(QCamera::Position position, QObject * parent = 0)
CaptureModes captureMode() const
Error error() const
QString errorString() const
QCameraExposure * exposure() const
QCameraFocus * focus() const
QCameraImageProcessing * imageProcessing() const
bool isCaptureModeSupported(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)
State state() const
Status status() const
QCamera::LockTypes supportedLocks() const

Reimplemented Public Functions

virtual QMultimedia::AvailabilityStatus availability() const

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)
  • 1 public slot inherited from QObject


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)

Additional Inherited Members

  • 11 static public members inherited from QObject
  • 2 protected functions inherited from QMediaObject
  • 9 protected functions inherited from QObject

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

QCamera::CaptureViewfinder0Camera is only configured to display viewfinder.
QCamera::CaptureStillImage0x01Camera is configured for still frames capture.
QCamera::CaptureVideo0x02Camera 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

QCamera::NoError0No errors have occurred.
QCamera::CameraError1An error has occurred.
QCamera::InvalidRequestError2System resource doesn't support requested functionality.
QCamera::ServiceMissingError3No camera service available.
QCamera::NotSupportedFeatureError4The feature is not supported.

enum QCamera::​LockChangeReason

QCamera::UserRequest0The lock status changed in result of user request, usually to unlock camera settings.
QCamera::LockAcquired1The lock status successfuly changed to QCamera::Locked.
QCamera::LockFailed2The camera failed to acquire the requested lock in result of autofocus failure, exposure out of supported range, etc.
QCamera::LockLost3The camera is not able to maintain the requested lock any more. Lock status is changed to QCamera::Unlocked.
QCamera::LockTemporaryLost4The 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

QCamera::Unlocked0The 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::Searching1The 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::Locked2The 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

QCamera::LockExposure0x01Lock camera exposure.
QCamera::LockWhiteBalance0x02Lock the white balance.
QCamera::LockFocus0x04Lock 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.

QCamera::UnspecifiedPosition0The camera position is unspecified or unknown.
QCamera::BackFace1The 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::FrontFace2The 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

QCamera::UnloadedState0The 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.

QCamera::LoadedState1The 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.

QCamera::ActiveState2In the active state as soon as camera is started the viewfinder displays video frames and the camera is ready for capture.

enum QCamera::​Status

QCamera::ActiveStatus8The 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::StartingStatus6The camera is starting in result of state transition to QCamera::ActiveState. The camera service is not ready to capture yet.
QCamera::StoppingStatus7The camera is stopping in result of state transition from QCamera::ActiveState to QCamera::LoadedState or QCamera::UnloadedState.
QCamera::StandbyStatus5The 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::LoadedStatus4The 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::LoadingStatus2The camera device loading in result of state transition from QCamera::UnloadedState to QCamera::LoadedState or QCamera::ActiveState.
QCamera::UnloadingStatus3The camera device is unloading in result of state transition from QCamera::LoadedState or QCamera::ActiveState to QCamera::UnloadedState.
QCamera::UnloadedStatus1The initial camera status, with camera not loaded. The camera capabilities including supported capture settings may be unknown.
QCamera::UnavailableStatus0The 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:

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:

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:

Status status() const

Notifier signal:

void statusChanged(QCamera::Status status)

Member Function Documentation

QCamera::​QCamera(QObject * parent = 0)

Construct a QCamera with a parent.

QCamera::​QCamera(const QByteArray & deviceName, QObject * parent = 0)

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 = 0)

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 = 0)

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.


Destroys the camera object.

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

Reimplemented from QMediaObject::availability().

Returns the availability state of the camera service.

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.

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(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.

[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.

[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.

[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.

[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.

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