QVideoFrame Class

The QVideoFrame class represents a frame of video data. More...

Header: #include <QVideoFrame>
CMake: find_package(Qt6 COMPONENTS Multimedia REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Multimedia)
qmake: QT += multimedia

Public Types

enum HandleType { NoHandle, RhiTextureHandle }
enum MapMode { NotMapped, ReadOnly, WriteOnly, ReadWrite }

Public Functions

QVideoFrame(QVideoFrame &&other)
QVideoFrame(const QVideoFrame &other)
QVideoFrame(const QVideoFrameFormat &format)
QVideoFrame()
QVideoFrame &operator=(const QVideoFrame &other)
QVideoFrame &operator=(QVideoFrame &&other)
~QVideoFrame()
uchar *bits(int plane)
const uchar *bits(int plane) const
int bytesPerLine(int plane) const
qint64 endTime() const
QVideoFrame::HandleType handleType() const
int height() const
bool isMapped() const
bool isReadable() const
bool isValid() const
bool isWritable() const
bool map(QVideoFrame::MapMode mode)
QVideoFrame::MapMode mapMode() const
int mappedBytes(int plane) const
void paint(QPainter *painter, const QRectF &rect, const QVideoFrame::PaintOptions &options)
QVideoFrameFormat::PixelFormat pixelFormat() const
int planeCount() const
void setEndTime(qint64 time)
void setStartTime(qint64 time)
void setSubtitleText(const QString &text)
QSize size() const
qint64 startTime() const
QString subtitleText() const
QVideoFrameFormat surfaceFormat() const
QImage toImage() const
void unmap()
int width() const
bool operator!=(const QVideoFrame &other) const
bool operator==(const QVideoFrame &other) const

Detailed Description

A QVideoFrame encapsulates the pixel data of a video frame, and information about the frame.

Video frames can come from several places - decoded media, a camera, or generated programmatically. The way pixels are described in these frames can vary greatly, and some pixel formats offer greater compression opportunities at the expense of ease of use.

The pixel contents of a video frame can be mapped to memory using the map() function. After a successful call to map(), the video data can be accessed through various functions. Some of the YUV pixel formats provide the data in several planes. The planeCount() method will return the amount of planes that being used.

While mapped, the video data of each plane can accessed using the bits() function, which returns a pointer to a buffer. The size of this buffer is given by the mappedBytes() function, and the size of each line is given by bytesPerLine(). The return value of the handle() function may also be used to access frame data using the internal buffer's native APIs (for example - an OpenGL texture handle).

A video frame can also have timestamp information associated with it. These timestamps can be used to determine when to start and stop displaying the frame.

QVideoFrame objects can consume a significant amount of memory or system resources and should not be held for longer than required by the application.

Note: Since video frames can be expensive to copy, QVideoFrame is explicitly shared, so any change made to a video frame will also apply to any copies.

Member Type Documentation

enum QVideoFrame::HandleType

Identifies the type of a video buffers handle.

ConstantValueDescription
QVideoFrame::NoHandle0The buffer has no handle, its data can only be accessed by mapping the buffer.
QVideoFrame::RhiTextureHandle1The handle of the buffer is defined by The Qt Rendering Hardware Interface (RHI). RHI is Qt's internal graphics abstraction for 3D APIs, such as OpenGL, Vulkan, Metal, and Direct 3D.

See also handleType().

enum QVideoFrame::MapMode

Enumerates how a video buffer's data is mapped to system memory.

ConstantValueDescription
QVideoFrame::NotMapped0x00The video buffer is not mapped to memory.
QVideoFrame::ReadOnly0x01The mapped memory is populated with data from the video buffer when mapped, but the content of the mapped memory may be discarded when unmapped.
QVideoFrame::WriteOnly0x02The mapped memory is uninitialized when mapped, but the possibly modified content will be used to populate the video buffer when unmapped.
QVideoFrame::ReadWriteReadOnly | WriteOnlyThe mapped memory is populated with data from the video buffer, and the video buffer is repopulated with the content of the mapped memory when it is unmapped.

See also mapMode() and map().

Member Function Documentation

QVideoFrame::QVideoFrame(QVideoFrame &&other)

Constructs a QVideoFrame by moving from other.

QVideoFrame::QVideoFrame(const QVideoFrame &other)

Constructs a shallow copy of other. Since QVideoFrame is explicitly shared, these two instances will reflect the same frame.

QVideoFrame::QVideoFrame(const QVideoFrameFormat &format)

Constructs a video frame of the given pixel format.

QVideoFrame::QVideoFrame()

Constructs a null video frame.

QVideoFrame &QVideoFrame::operator=(const QVideoFrame &other)

Assigns the contents of other to this video frame. Since QVideoFrame is explicitly shared, these two instances will reflect the same frame.

QVideoFrame &QVideoFrame::operator=(QVideoFrame &&other)

Moves other into this QVideoFrame.

QVideoFrame::~QVideoFrame()

Destroys a video frame.

uchar *QVideoFrame::bits(int plane)

Returns a pointer to the start of the frame data buffer for a plane.

This value is only valid while the frame data is mapped.

Changes made to data accessed via this pointer (when mapped with write access) are only guaranteed to have been persisted when unmap() is called and when the buffer has been mapped for writing.

See also map(), mappedBytes(), bytesPerLine(), and planeCount().

const uchar *QVideoFrame::bits(int plane) const

Returns a pointer to the start of the frame data buffer for a plane.

This value is only valid while the frame data is mapped.

If the buffer was not mapped with read access, the contents of this buffer will initially be uninitialized.

See also map(), mappedBytes(), bytesPerLine(), and planeCount().

int QVideoFrame::bytesPerLine(int plane) const

Returns the number of bytes in a scan line of a plane.

This value is only valid while the frame data is mapped.

See also bits(), map(), mappedBytes(), and planeCount().

qint64 QVideoFrame::endTime() const

Returns the presentation time (in microseconds) when a frame should stop being displayed.

An invalid time is represented as -1.

See also setEndTime().

QVideoFrame::HandleType QVideoFrame::handleType() const

Returns the type of a video frame's handle.

The handle type could either be NoHandle, meaning that the frame is memory based, or a RHI texture.

int QVideoFrame::height() const

Returns the height of a video frame.

bool QVideoFrame::isMapped() const

Identifies if a video frame's contents are currently mapped to system memory.

This is a convenience function which checks that the MapMode of the frame is not equal to QVideoFrame::NotMapped.

Returns true if the contents of the video frame are mapped to system memory, and false otherwise.

See also mapMode() and QVideoFrame::MapMode.

bool QVideoFrame::isReadable() const

Identifies if the mapped contents of a video frame were read from the frame when it was mapped.

This is a convenience function which checks if the MapMode contains the QVideoFrame::WriteOnly flag.

Returns true if the contents of the mapped memory were read from the video frame, and false otherwise.

See also mapMode() and QVideoFrame::MapMode.

bool QVideoFrame::isValid() const

Identifies whether a video frame is valid.

An invalid frame has no video buffer associated with it.

Returns true if the frame is valid, and false if it is not.

bool QVideoFrame::isWritable() const

Identifies if the mapped contents of a video frame will be persisted when the frame is unmapped.

This is a convenience function which checks if the MapMode contains the QVideoFrame::WriteOnly flag.

Returns true if the video frame will be updated when unmapped, and false otherwise.

Note: The result of altering the data of a frame that is mapped in read-only mode is undefined. Depending on the buffer implementation the changes may be persisted, or worse alter a shared buffer.

See also mapMode() and QVideoFrame::MapMode.

bool QVideoFrame::map(QVideoFrame::MapMode mode)

Maps the contents of a video frame to system (CPU addressable) memory.

In some cases the video frame data might be stored in video memory or otherwise inaccessible memory, so it is necessary to map a frame before accessing the pixel data. This may involve copying the contents around, so avoid mapping and unmapping unless required.

The map mode indicates whether the contents of the mapped memory should be read from and/or written to the frame. If the map mode includes the QVideoFrame::ReadOnly flag the mapped memory will be populated with the content of the video frame when initially mapped. If the map mode includes the QVideoFrame::WriteOnly flag the content of the possibly modified mapped memory will be written back to the frame when unmapped.

While mapped the contents of a video frame can be accessed directly through the pointer returned by the bits() function.

When access to the data is no longer needed, be sure to call the unmap() function to release the mapped memory and possibly update the video frame contents.

If the video frame has been mapped in read only mode, it is permissible to map it multiple times in read only mode (and unmap it a corresponding number of times). In all other cases it is necessary to unmap the frame first before mapping a second time.

Note: Writing to memory that is mapped as read-only is undefined, and may result in changes to shared data or crashes.

Returns true if the frame was mapped to memory in the given mode and false otherwise.

See also unmap(), mapMode(), and bits().

QVideoFrame::MapMode QVideoFrame::mapMode() const

Returns the mode a video frame was mapped to system memory in.

See also map() and QVideoFrame::MapMode.

int QVideoFrame::mappedBytes(int plane) const

Returns the number of bytes occupied by plane plane of the mapped frame data.

This value is only valid while the frame data is mapped.

See also map().

void QVideoFrame::paint(QPainter *painter, const QRectF &rect, const QVideoFrame::PaintOptions &options)

Uses a QPainter, painter, to render this QVideoFrame to rect. The PaintOptions options can be used to specify a background color and how rect should be filled with the video.

Note: that rendering will usually happen without hardware acceleration when using this method.

QVideoFrameFormat::PixelFormat QVideoFrame::pixelFormat() const

Returns the pixel format of this video frame.

int QVideoFrame::planeCount() const

Returns the number of planes in the video frame.

See also map().

void QVideoFrame::setEndTime(qint64 time)

Sets the presentation time (in microseconds) when a frame should stop being displayed.

An invalid time is represented as -1.

See also endTime().

void QVideoFrame::setStartTime(qint64 time)

Sets the presentation time (in microseconds) when the frame should initially be displayed.

An invalid time is represented as -1.

See also startTime().

void QVideoFrame::setSubtitleText(const QString &text)

Sets the subtitle text that should be rendered together with this video frame to text.

See also subtitleText().

QSize QVideoFrame::size() const

Returns the dimensions of a video frame.

qint64 QVideoFrame::startTime() const

Returns the presentation time (in microseconds) when the frame should be displayed.

An invalid time is represented as -1.

See also setStartTime().

QString QVideoFrame::subtitleText() const

Returns the subtitle text that should be rendered together with this video frame.

See also setSubtitleText().

QVideoFrameFormat QVideoFrame::surfaceFormat() const

Returns the surface format of this video frame.

QImage QVideoFrame::toImage() const

Based on the pixel format converts current video frame to image.

void QVideoFrame::unmap()

Releases the memory mapped by the map() function.

If the MapMode included the QVideoFrame::WriteOnly flag this will persist the current content of the mapped memory to the video frame.

unmap() should not be called if map() function failed.

See also map().

int QVideoFrame::width() const

Returns the width of a video frame.

bool QVideoFrame::operator!=(const QVideoFrame &other) const

Returns true if this QVideoFrame and other do not reflect the same frame.

bool QVideoFrame::operator==(const QVideoFrame &other) const

Returns true if this QVideoFrame and other reflect the same frame.

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