OpenCV  3.3.1-dev
Open Source Computer Vision
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cv::VideoWriter Class Reference

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)
 
 VideoWriter (const String &filename, int apiPreference, 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...
 
bool open (const String &filename, int apiPreference, int fourcc, double fps, Size frameSize, bool isColor=true)
 
virtual VideoWriteroperator<< (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< CvVideoWriterwriter
 

Detailed Description

Video writer class.

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

Examples:
hog.cpp, and videowriter_basic.cpp.

Constructor & Destructor Documentation

§ VideoWriter() [1/3]

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() [2/3]

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
filenameName of the output video file.
fourcc4-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.
fpsFramerate of the created video stream.
frameSizeSize of the video frames.
isColorIf 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() [3/3]

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()

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
propIdProperty 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.

Examples:
hog.cpp, and videowriter_basic.cpp.

§ open() [1/2]

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:
hog.cpp, and videowriter_basic.cpp.

§ open() [2/2]

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.

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

Examples:
videowriter_basic.cpp.

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: