Contents

QMediaRecorder Class

The QMediaRecorder class is used for encoding and recording a capture session. More...

Header: #include <QMediaRecorder>
CMake: find_package(Qt6 REQUIRED COMPONENTS Multimedia)
target_link_libraries(mytarget PRIVATE Qt6::Multimedia)
qmake: QT += multimedia
In QML: MediaRecorder
Inherits: QObject

Public Types

enum EncodingMode { ConstantQualityEncoding, ConstantBitRateEncoding, AverageBitRateEncoding, TwoPassEncoding }
enum Error { NoError, ResourceError, FormatError, OutOfSpaceError, LocationNotWritable }
enum Quality { VeryLowQuality, LowQuality, NormalQuality, HighQuality, VeryHighQuality }
enum RecorderState { StoppedState, RecordingState, PausedState }

Properties

Public Functions

QMediaRecorder(QObject *parent = nullptr)
virtual ~QMediaRecorder()
QUrl actualLocation() const
void addMetaData(const QMediaMetaData &metaData)
int audioBitRate() const
int audioChannelCount() const
int audioSampleRate() const
bool autoStop() const
QMediaCaptureSession *captureSession() const
qint64 duration() const
QMediaRecorder::EncodingMode encodingMode() const
QMediaRecorder::Error error() const
QString errorString() const
bool isAvailable() const
QMediaFormat mediaFormat() const
QMediaMetaData metaData() const
QIODevice *outputDevice() const
QUrl outputLocation() const
QMediaRecorder::Quality quality() const
QMediaRecorder::RecorderState recorderState() const
void setAudioBitRate(int bitRate)
void setAudioChannelCount(int channels)
void setAudioSampleRate(int sampleRate)
void setAutoStop(bool autoStop)
void setEncodingMode(QMediaRecorder::EncodingMode mode)
void setMediaFormat(const QMediaFormat &format)
void setMetaData(const QMediaMetaData &metaData)
void setOutputDevice(QIODevice *device)
void setOutputLocation(const QUrl &location)
void setQuality(QMediaRecorder::Quality quality)
void setVideoBitRate(int bitRate)
void setVideoFrameRate(qreal frameRate)
void setVideoResolution(const QSize &size)
void setVideoResolution(int width, int height)
int videoBitRate() const
qreal videoFrameRate() const
QSize videoResolution() const

Public Slots

void pause()
void record()
void stop()

Signals

void actualLocationChanged(const QUrl &location)
void audioBitRateChanged()
void audioChannelCountChanged()
void audioSampleRateChanged()
void autoStopChanged()
void durationChanged(qint64 duration)
void encoderSettingsChanged()
void encodingModeChanged()
void errorChanged()
void errorOccurred(QMediaRecorder::Error error, const QString &errorString)
void mediaFormatChanged()
void metaDataChanged()
void qualityChanged()
void recorderStateChanged(QMediaRecorder::RecorderState state)
void videoBitRateChanged()
void videoFrameRateChanged()
void videoResolutionChanged()

Detailed Description

Use the QMediaRecorder class to encode and record media generated in QMediaCaptureSession. You can generate:

To record media, connect a generator to a corresponding media capture session.

Performance of video encoding and recording is limited by the hardware, the operating system, the installed graphic drivers, and the input video format. If QCamera, QScreenCapture, or QWindowCapture produces video frames faster than QMediaRecorder can encode and record them, the recorder may drop some frames. This is likely to occur if the input frame resolution is high, 4K for example, and hardware-accelerated encoding is unavailable. If you generate input video via QVideoFrameInput, the method QVideoFrameInput::sendVideoFrame will do nothing and return false whenever this limitation is reached and the internal frame queue is full. Rely on the signal QVideoFrameInput::readyToSendVideoFrame to know when the recorder is ready to receive new frames again. If you cannot change the rate of video frame generation and dropping frames is undesirable, we recommend implementing your own frame queue on top of QVideoFrameInput, considering the memory limitations of the hardware.

 QMediaCaptureSession session;
 QAudioInput audioInput;
 session.setAudioInput(&input);
 QMediaRecorder recorder;
 session.setRecorder(&recorder);
 recorder.setQuality(QMediaRecorder::HighQuality);
 recorder.setOutputLocation(QUrl::fromLocalFile("test.mp3"));
 recorder.record();

Member Type Documentation

enum QMediaRecorder::EncodingMode

Enumerates encoding modes.

ConstantValueDescription
QMediaRecorder::ConstantQualityEncoding0Encoding will aim to have a constant quality, adjusting bitrate to fit.
QMediaRecorder::ConstantBitRateEncoding1Encoding will use a constant bit rate, adjust quality to fit.
QMediaRecorder::AverageBitRateEncoding2Encoding will try to keep an average bitrate setting, but will use more or less as needed.
QMediaRecorder::TwoPassEncoding3The media will first be processed to determine the characteristics, and then processed a second time allocating more bits to the areas that need it.

enum QMediaRecorder::Error

ConstantValueDescription
QMediaRecorder::NoError0No Errors.
QMediaRecorder::ResourceError1Device is not ready or not available.
QMediaRecorder::FormatError2Current format is not supported.
QMediaRecorder::OutOfSpaceError3No space left on device.
QMediaRecorder::LocationNotWritable4The output location is not writable.

enum QMediaRecorder::Quality

Enumerates quality encoding levels.

ConstantValue
QMediaRecorder::VeryLowQuality0
QMediaRecorder::LowQuality1
QMediaRecorder::NormalQuality2
QMediaRecorder::HighQuality3
QMediaRecorder::VeryHighQuality4

enum QMediaRecorder::RecorderState

ConstantValueDescription
QMediaRecorder::StoppedState0The recorder is not active.
QMediaRecorder::RecordingState1The recording is requested.
QMediaRecorder::PausedState2The recorder is paused.

Property Documentation

[read-only] actualLocation : const QUrl

This property holds the actual location of the last media content.

The actual location is reset when a new outputLocation or a non-null outputDevice is assigned. When record() is invoked and outputDevice is null or not writable, the recorder generates the actual location basing on the following rules.

  • If outputLocation is empty, a directory, or a file without an extension, the recorder generates the appropriate extension based on the selected media format and system MIME types.
  • If outputLocation is a directory, the recorder generates a new file name within it.
  • If outputLocation is empty, the recorder generates a new file name in the system-specific directory for audio or video.
  • The recorder generates the actual location before emitting recorderStateChanged(RecordingState).

Access functions:

QUrl actualLocation() const

Notifier signal:

void actualLocationChanged(const QUrl &location)

autoStop : bool

This property controls whether the media recorder stops automatically when all media inputs have reported the end of the stream or have been deactivated.

The end of the stream is reported by sending an empty media frame, which you can send explicitly via QVideoFrameInput or QAudioBufferInput.

Video inputs, specificly, QCamera, QScreenCapture and QWindowCapture, can be deactivated via the function setActive.

Defaults to false.

QMediaRecorder::autoStop is only supported with the FFmpeg backend.

Access functions:

bool autoStop() const
void setAutoStop(bool autoStop)

Notifier signal:

void autoStopChanged()

See also QCamera, QScreenCapture, and QWindowCapture.

[read-only] duration : const qint64

This property holds the recorded media duration in milliseconds.

Access functions:

qint64 duration() const

Notifier signal:

void durationChanged(qint64 duration)

[read-only] error : const QMediaRecorder::Error

Returns the current error state.

Access functions:

QMediaRecorder::Error error() const

Notifier signal:

void errorChanged()

See also errorString().

[read-only] errorString : const QString

Returns a string describing the current error state.

Access functions:

QString errorString() const

Notifier signal:

void errorChanged()

See also error().

mediaFormat : QMediaFormat

Returns the recording media format.

Access functions:

QMediaFormat mediaFormat() const
void setMediaFormat(const QMediaFormat &format)

Notifier signal:

void mediaFormatChanged()

metaData : QMediaMetaData

Returns the metaData associated with the recording.

Access functions:

QMediaMetaData metaData() const
void setMetaData(const QMediaMetaData &metaData)

Notifier signal:

void metaDataChanged()

outputLocation : QUrl

This property holds the destination location of media content.

Setting the location can fail, for example when the service supports only local file system locations but a network URL was passed. If the operation fails, the errorOccured() signal is emitted.

The output location is ignored if a writable outputDevice has been assigned to the recorder. This behavior may change in the future, so we recommend setting only one output, either outputLocation or outputDevice.

The output location can be empty, a directory, or a file. The path to a directory or file can be relative or absolute. The record() method generates the actual location according to the specified output location and system-specific settings. Refer to the actualLocation property description for details.

Access functions:

QUrl outputLocation() const
void setOutputLocation(const QUrl &location)

See also actualLocation and outputDevice().

quality : Quality

Returns the recording quality.

Access functions:

QMediaRecorder::Quality quality() const
void setQuality(QMediaRecorder::Quality quality)

Notifier signal:

void qualityChanged()

[read-only] recorderState : const QMediaRecorder::RecorderState

This property holds the current state of the media recorder.

The state property represents the user request and is changed synchronously during record(), pause() or stop() calls. Recorder state may also change asynchronously when recording fails.

Access functions:

QMediaRecorder::RecorderState recorderState() const

Notifier signal:

void recorderStateChanged(QMediaRecorder::RecorderState state)

Member Function Documentation

QMediaRecorder::QMediaRecorder(QObject *parent = nullptr)

Constructs a media recorder. The media recorder is a child of parent.

[virtual noexcept] QMediaRecorder::~QMediaRecorder()

Destroys a media recorder object.

[signal] void QMediaRecorder::actualLocationChanged(const QUrl &location)

Signals that the actual location of the recorded media has changed. This signal is usually emitted when recording starts.

Note: Notifier signal for property actualLocation.

void QMediaRecorder::addMetaData(const QMediaMetaData &metaData)

Adds metaData to the recorded media.

int QMediaRecorder::audioBitRate() const

Returns the bit rate of the compressed audio stream in bits per second.

Note: Getter function for property audioBitRate.

See also setAudioBitRate().

[signal] void QMediaRecorder::audioBitRateChanged()

Signals when the recording audio bit rate changes.

Note: Notifier signal for property audioBitRate.

int QMediaRecorder::audioChannelCount() const

Returns the number of audio channels.

Note: Getter function for property audioChannelCount.

See also setAudioChannelCount().

[signal] void QMediaRecorder::audioChannelCountChanged()

Signals when the recording audio channel count changes.

Note: Notifier signal for property audioChannelCount.

int QMediaRecorder::audioSampleRate() const

Returns the audio sample rate in Hz.

Note: Getter function for property audioSampleRate.

See also setAudioSampleRate().

[signal] void QMediaRecorder::audioSampleRateChanged()

Signals when the recording audio sample rate changes.

Note: Notifier signal for property audioSampleRate.

QMediaCaptureSession *QMediaRecorder::captureSession() const

Returns the media capture session.

[signal] void QMediaRecorder::durationChanged(qint64 duration)

Signals that the duration of the recorded media has changed.

Note: Notifier signal for property duration.

[signal] void QMediaRecorder::encoderSettingsChanged()

Signals when the encoder settings change.

QMediaRecorder::EncodingMode QMediaRecorder::encodingMode() const

Returns the encoding mode.

Note: Getter function for property encodingMode.

See also setEncodingMode() and EncodingMode.

[signal] void QMediaRecorder::encodingModeChanged()

Signals when the encoding mode changes.

Note: Notifier signal for property encodingMode.

[signal] void QMediaRecorder::errorOccurred(QMediaRecorder::Error error, const QString &errorString)

Signals that an error has occurred, with errorString containing a description of the error.

bool QMediaRecorder::isAvailable() const

Returns true if media recorder service ready to use.

[signal] void QMediaRecorder::metaDataChanged()

Signals that a media object's meta-data has changed.

If multiple meta-data elements are changed metaDataChanged() is emitted once.

Note: Notifier signal for property metaData.

QIODevice *QMediaRecorder::outputDevice() const

Returns the output IO device for media content.

See also setOutputDevice().

[slot] void QMediaRecorder::pause()

Pauses recording.

The recorder state is changed to QMediaRecorder::PausedState.

Depending on the platform, pausing recording may be not supported. In this case the recorder state is unchanged.

[signal] void QMediaRecorder::qualityChanged()

Signals when the recording quality changes.

Note: Notifier signal for property quality.

[slot] void QMediaRecorder::record()

Starts recording.

While the recorder state is changed immediately to c{QMediaRecorder::RecordingState}, recording may start asynchronously.

If recording fails error() signal is emitted with recorder state being reset back to QMediaRecorder::StoppedState.

This method updates actualLocation according to its generation rules.

Note: On mobile devices, recording will happen in the orientation the device had when calling record and is locked for the duration of the recording. To avoid artifacts on the user interface, we recommend to keep the user interface locked to the same orientation as long as the recording is ongoing using the contentOrientation property of QWindow and unlock it again once the recording is finished.

QMediaRecorder::RecorderState QMediaRecorder::recorderState() const

Returns the current media recorder state.

Note: Getter function for property recorderState.

See also QMediaRecorder::RecorderState.

[signal] void QMediaRecorder::recorderStateChanged(QMediaRecorder::RecorderState state)

Signals that a media recorder's state has changed.

Note: Notifier signal for property recorderState.

void QMediaRecorder::setAudioBitRate(int bitRate)

Sets the audio bitRate in bits per second.

Note: Setter function for property audioBitRate.

See also audioBitRate().

void QMediaRecorder::setAudioChannelCount(int channels)

Sets the number of audio channels.

A value of -1 indicates the recorder should make an optimal choice based on what is available from the audio source and the limitations of the codec.

Note: Setter function for property audioChannelCount.

See also audioChannelCount().

void QMediaRecorder::setAudioSampleRate(int sampleRate)

Sets the audio sampleRate in Hz.

A value of -1 indicates the recorder should make an optimal choice based on what is available from the audio source, and the limitations of the codec.

Note: Setter function for property audioSampleRate.

See also audioSampleRate().

void QMediaRecorder::setEncodingMode(QMediaRecorder::EncodingMode mode)

Sets the encoding mode setting.

If ConstantQualityEncoding is set, the quality encoding parameter is used and bit rates are ignored, otherwise the bitrates are used.

Note: Setter function for property encodingMode.

See also encodingMode() and EncodingMode.

void QMediaRecorder::setMetaData(const QMediaMetaData &metaData)

Sets the meta data to metaData.

Note: To ensure that meta-data is set correctly, it should be set before starting the recording. Once the recording is started, any meta-data set will be attached to the next recording.

Note: Setter function for property metaData.

See also metaData().

void QMediaRecorder::setOutputDevice(QIODevice *device)

Set the output IO device for media content.

The device must have been opened in the WriteOnly or ReadWrite modes before the recording starts.

The media recorder doesn't take ownership of the specified device. If the recording has been started, the device must be kept alive and open until the signal recorderStateChanged(StoppedState) is emitted.

This method resets actualLocation immediately unless the specified device is null.

If a writable output device is assigned to the recorder, outputLocation is ignored, and actualLocation is not generated when recording starts. This behavior may change in the future, so we recommend setting only one output, either outputLocation or outputDevice.

QMediaRecorder::setOutputDevice is only supported with the FFmpeg backend.

See also outputDevice() and outputLocation.

void QMediaRecorder::setVideoBitRate(int bitRate)

Sets the video bitRate in bits per second.

Note: Setter function for property videoBitRate.

See also videoBitRate().

void QMediaRecorder::setVideoFrameRate(qreal frameRate)

Sets the video frameRate.

A value of 0 indicates the recorder should make an optimal choice based on what is available from the video source and the limitations of the codec.

Note: Setter function for property videoFrameRate.

See also videoFrameRate().

void QMediaRecorder::setVideoResolution(const QSize &size)

Sets the resolution of the encoded video to size.

Pass an empty QSize to make the recorder choose an optimal resolution based on what is available from the video source and the limitations of the codec.

Note: Setter function for property videoResolution.

See also videoResolution().

void QMediaRecorder::setVideoResolution(int width, int height)

Sets the width and height of the resolution of the encoded video.

This is an overloaded function.

Note: Setter function for property videoResolution.

[slot] void QMediaRecorder::stop()

The recorder will stop the recording. Processing pending video and audio data might however still take some time. The recording is finished, once the state of the media recorder changes to QMediaRecorder::StoppedState.

int QMediaRecorder::videoBitRate() const

Returns the bit rate of the compressed video stream in bits per second.

Note: Getter function for property videoBitRate.

See also setVideoBitRate().

[signal] void QMediaRecorder::videoBitRateChanged()

Signals when the recording video bit rate changes.

Note: Notifier signal for property videoBitRate.

qreal QMediaRecorder::videoFrameRate() const

Returns the video frame rate.

Note: Getter function for property videoFrameRate.

See also setVideoFrameRate().

[signal] void QMediaRecorder::videoFrameRateChanged()

Signals when the recording video frame rate changes.

Note: Notifier signal for property videoFrameRate.

QSize QMediaRecorder::videoResolution() const

Returns the resolution of the encoded video.

Note: Getter function for property videoResolution.

See also setVideoResolution().

[signal] void QMediaRecorder::videoResolutionChanged()

Signals when the video recording resolution changes.

Note: Notifier signal for property videoResolution.

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