Video writer class. More...

#include "videoio.hpp"

Public Member Functions
	VideoWriter ()
	Default constructors. More...

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

virtual	~VideoWriter ()
	Default destructor. More...

virtual double	get (int propId) const
	Returns the specified VideoWriter property. More...

virtual bool	isOpened () const
	Returns true if video writer has been successfully initialized. More...

virtual bool	open (const String &filename, int fourcc, double fps, Size frameSize, bool isColor=true)
	Initializes or reinitializes video writer. More...

virtual VideoWriter &	operator<< (const Mat &image)
	Stream operator to write the next video frame. More...

virtual void	release ()
	Closes the video writer. More...

virtual bool	set (int propId, double value)
	Sets a property in the VideoWriter. More...

virtual void	write (const Mat &image)
	Writes the next video frame. More...

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

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.

Here is how the class can be used:

#include <opencv2/opencv.hpp>
#include <iostream>
#include <stdio.h>
using namespace cv;
using namespace std;
int main(int, char**)
{
    Mat src;
    // use default camera as video source
    VideoCapture cap(0);
    // check if we succeeded
    if (!cap.isOpened()) {
        cerr << "ERROR! Unable to open camera\n";
        return -1;
    }
    // get one frame from camera to know frame size and type
    cap >> src;
    // check if we succeeded
    if (src.empty()) {
        cerr << "ERROR! blank frame grabbed\n";
        return -1;
    }
    bool isColor = (src.type() == CV_8UC3);
    //--- INITIALIZE VIDEOWRITER
    VideoWriter writer;
    int codec = CV_FOURCC('M', 'J', 'P', 'G');  // select desired codec (must be available at runtime)
    double fps = 25.0;                          // framerate of the created video stream
    string filename = "./live.avi";             // name of the output video file
    writer.open(filename, codec, fps, src.size(), isColor);
    // check if we succeeded
    if (!writer.isOpened()) {
        cerr << "Could not open the output video file for write\n";
        return -1;
    }
    //--- GRAB AND WRITE LOOP
    cout << "Writing videofile: " << filename << endl
         << "Press any key to terminate" << endl;
    for (;;)
    {
        // check if we succeeded
        if (!cap.read(src)) {
            cerr << "ERROR! blank frame grabbed\n";
            break;
        }
        // encode the frame into the videofile stream
        writer.write(src);
        // show live and wait for a key with timeout long enough to show images
        imshow("Live", src);
        if (waitKey(5) >= 0)
            break;
    }
    // the videofile will be closed and released automatically in VideoWriter destructor
    return 0;
}

Constructor & Destructor Documentation

§ VideoWriter() [1/2]

cv::VideoWriter::VideoWriter ( )

Default constructors.

The constructors/functions initialize video writers.

On Linux FFMPEG is used to write videos;
On Windows FFMPEG or VFW is used;
On MacOSX QTKit is used.

§ VideoWriter() [2/2]

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 Video Codecs by FOURCC page. 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 (the flag is currently supported on Windows only).

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.

§ ~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.

§ isOpened()

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

virtual

Returns true if video writer has been successfully initialized.

§ open()

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.

§ operator<<()

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

virtual

Stream operator to write the next video frame.

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 ( const Mat & image )

virtual

Writes the next video frame.

Parameters

image The written frame

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.

Member Data Documentation

§ iwriter

Ptr<IVideoWriter> cv::VideoWriter::iwriter

protected

§ writer

Ptr<CvVideoWriter> cv::VideoWriter::writer

protected

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

videoio/include/opencv2/videoio.hpp

Public Member Functions

Static Public Member Functions

Static Protected Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

§ VideoWriter() [1/2]

§ VideoWriter() [2/2]

§ ~VideoWriter()

Member Function Documentation

§ create()

§ fourcc()

§ get()

§ isOpened()

§ open()

§ operator<<()

§ release()

§ set()

§ write()

Member Data Documentation

§ iwriter

§ writer