cv::VideoWriter Class Reference

Video writer class. More...

#include <opencv2/videoio.hpp>

Public Member Functions
	VideoWriter ()
	Default constructors.
	VideoWriter (const String &filename, int apiPreference, int fourcc, double fps, const Size &frameSize, const std::vector< int > &params)
	VideoWriter (const String &filename, int apiPreference, int fourcc, double fps, Size frameSize, bool isColor=true)
	VideoWriter (const String &filename, int fourcc, double fps, const Size &frameSize, const std::vector< int > &params)
	VideoWriter (const String &filename, int fourcc, double fps, Size frameSize, bool isColor=true)
virtual	~VideoWriter ()
	Default destructor.
virtual double	get (int propId) const
	Returns the specified VideoWriter property.
String	getBackendName () const
	Returns used backend API name.
virtual bool	isOpened () const
	Returns true if video writer has been successfully initialized.
bool	open (const String &filename, int apiPreference, int fourcc, double fps, const Size &frameSize, const std::vector< int > &params)
bool	open (const String &filename, int apiPreference, int fourcc, double fps, Size frameSize, bool isColor=true)
bool	open (const String &filename, int fourcc, double fps, const Size &frameSize, const std::vector< int > &params)
virtual bool	open (const String &filename, int fourcc, double fps, Size frameSize, bool isColor=true)
	Initializes or reinitializes video writer.
virtual VideoWriter &	operator<< (const Mat &image)
	Stream operator to write the next video frame.
virtual VideoWriter &	operator<< (const UMat &image)
virtual void	release ()
	Closes the video writer.
virtual bool	set (int propId, double value)
	Sets a property in the VideoWriter.
virtual void	write (InputArray image)
	Writes the next video frame.

Static Public Member Functions
static int	fourcc (char c1, char c2, char c3, char c4)
	Concatenates 4 chars to a fourcc code.

Static Protected Member Functions
static Ptr< IVideoWriter >	create (const String &filename, int fourcc, double fps, Size frameSize, bool isColor=true)

Protected Attributes
Ptr< IVideoWriter >	iwriter
Ptr< CvVideoWriter >	writer

Detailed Description

Video writer class.

The class provides C++ API for writing video files or image sequences.

Examples

samples/cpp/tutorial_code/videoio/video-write/video-write.cpp, samples/cpp/videowriter_basic.cpp, and samples/tapi/hog.cpp.

Constructor & Destructor Documentation

VideoWriter() [1/5]

cv::VideoWriter::VideoWriter

(

)

Default constructors.

The constructors/functions initialize video writers.

• On Linux FFMPEG is used to write videos;
• On Windows FFMPEG or MSWF or DSHOW is used;
• On MacOSX AVFoundation is used.

VideoWriter() [2/5]

cv::VideoWriter::VideoWriter	(	const String &	filename,
		int	fourcc,
		double	fps,
		Size	frameSize,
		bool	isColor = true
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Parameters

filename	Name of the output video file.
fourcc	4-character code of codec used to compress the frames. For example, VideoWriter::fourcc('P','I','M','1') is a MPEG-1 codec, VideoWriter::fourcc('M','J','P','G') is a motion-jpeg codec etc. List of codes can be obtained at MSDN page or with this archived page of the fourcc site for a more complete list). FFMPEG backend with MP4 container natively uses other values as fourcc code: see ObjectType, so you may receive a warning message from OpenCV about fourcc code conversion.
fps	Framerate of the created video stream.
frameSize	Size of the video frames.
isColor	If it is not zero, the encoder will expect and encode color frames, otherwise it will work with grayscale frames.

Tips:

• With some backends fourcc=-1 pops up the codec selection dialog from the system.
• To save image sequence use a proper filename (eg. img_%02d.jpg) and fourcc=0 OR fps=0. Use uncompressed image format (eg. img_%02d.BMP) to save raw frames.
• Most codecs are lossy. If you want lossless video file you need to use a lossless codecs (eg. FFMPEG FFV1, Huffman HFYU, Lagarith LAGS, etc...)
• If FFMPEG is enabled, using codec=0; fps=0; you can create an uncompressed (raw) video file.
• If FFMPEG is used, we allow frames of odd width or height, but in this case we truncate the rightmost column/the bottom row. Probably, this should be handled more elegantly, but some internal functions inside FFMPEG swscale require even width/height.

VideoWriter() [3/5]

cv::VideoWriter::VideoWriter	(	const String &	filename,
		int	apiPreference,
		int	fourcc,
		double	fps,
		Size	frameSize,
		bool	isColor = true
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. The apiPreference parameter allows to specify API backends to use. Can be used to enforce a specific reader implementation if multiple are available: e.g. cv::CAP_FFMPEG or cv::CAP_GSTREAMER.

VideoWriter() [4/5]

cv::VideoWriter::VideoWriter	(	const String &	filename,
		int	fourcc,
		double	fps,
		const Size &	frameSize,
		const std::vector< int > &	params
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts. The params parameter allows to specify extra encoder parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ... .) see cv::VideoWriterProperties

VideoWriter() [5/5]

cv::VideoWriter::VideoWriter	(	const String &	filename,
		int	apiPreference,
		int	fourcc,
		double	fps,
		const Size &	frameSize,
		const std::vector< int > &	params
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

~VideoWriter()

virtual cv::VideoWriter::~VideoWriter ( )

virtual

Default destructor.

The method first calls VideoWriter::release to close the already opened file.

Member Function Documentation

create()

static Ptr< IVideoWriter > cv::VideoWriter::create ( const String &  filename, int  fourcc, double  fps, Size  frameSize, bool  isColor = true  )

staticprotected

fourcc()

static int cv::VideoWriter::fourcc ( char  c1, char  c2, char  c3, char  c4  )

static

Concatenates 4 chars to a fourcc code.

Returns

a fourcc code

This static method constructs the fourcc code of the codec to be used in the constructor VideoWriter::VideoWriter or VideoWriter::open.

get()

virtual double cv::VideoWriter::get ( int  propId ) const

virtual

Returns the specified VideoWriter property.

Parameters

propId

Property identifier from cv::VideoWriterProperties (eg. cv::VIDEOWRITER_PROP_QUALITY) or one of Additional flags for video I/O API backends

Returns

Value for the specified property. Value 0 is returned when querying a property that is not supported by the backend used by the VideoWriter instance.

getBackendName()

String cv::VideoWriter::getBackendName

(

)

const

Returns used backend API name.

Note

Stream should be opened.

isOpened()

virtual bool cv::VideoWriter::isOpened ( ) const

virtual

Returns true if video writer has been successfully initialized.

Examples

samples/cpp/tutorial_code/videoio/video-write/video-write.cpp, samples/cpp/videowriter_basic.cpp, and samples/tapi/hog.cpp.

open() [1/4]

bool cv::VideoWriter::open	(	const String &	filename,
		int	apiPreference,
		int	fourcc,
		double	fps,
		const Size &	frameSize,
		const std::vector< int > &	params
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

open() [2/4]

bool cv::VideoWriter::open	(	const String &	filename,
		int	apiPreference,
		int	fourcc,
		double	fps,
		Size	frameSize,
		bool	isColor = true
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

open() [3/4]

bool cv::VideoWriter::open	(	const String &	filename,
		int	fourcc,
		double	fps,
		const Size &	frameSize,
		const std::vector< int > &	params
	)

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

open() [4/4]

virtual bool cv::VideoWriter::open ( const String &  filename, int  fourcc, double  fps, Size  frameSize, bool  isColor = true  )

virtual

Initializes or reinitializes video writer.

The method opens video writer. Parameters are the same as in the constructor VideoWriter::VideoWriter.

Returns

true if video writer has been successfully initialized

The method first calls VideoWriter::release to close the already opened file.

Examples

samples/cpp/tutorial_code/videoio/video-write/video-write.cpp, samples/cpp/videowriter_basic.cpp, and samples/tapi/hog.cpp.

operator<<() [1/2]

virtual VideoWriter & cv::VideoWriter::operator<< ( const Mat &  image )

virtual

Stream operator to write the next video frame.

See also

write

operator<<() [2/2]

virtual VideoWriter & cv::VideoWriter::operator<< ( const UMat &  image )

virtual

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

See also

write

release()

virtual void cv::VideoWriter::release ( )

virtual

Closes the video writer.

The method is automatically called by subsequent VideoWriter::open and by the VideoWriter destructor.

set()

virtual bool cv::VideoWriter::set ( int  propId, double  value  )

virtual

Sets a property in the VideoWriter.

Parameters

propId	Property identifier from cv::VideoWriterProperties (eg. cv::VIDEOWRITER_PROP_QUALITY) or one of Additional flags for video I/O API backends
value	Value of the property.

Returns

true if the property is supported by the backend used by the VideoWriter instance.

write()

virtual void cv::VideoWriter::write ( InputArray  image )

virtual

Writes the next video frame.

Parameters

image

The written frame. In general, color images are expected in BGR format.

The function/method writes the specified image to video file. It must have the same size as has been specified when opening the video writer.

Examples

samples/cpp/videowriter_basic.cpp.

Member Data Documentation

iwriter

Ptr<IVideoWriter> cv::VideoWriter::iwriter

protected

writer

Ptr<CvVideoWriter> cv::VideoWriter::writer

protected

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The documentation for this class was generated from the following file:

• opencv2/videoio.hpp