Class for video capturing from video files, image sequences or cameras. More...

#include <videoio.hpp>

Public Member Functions
CV_WRAP	VideoCapture ()
CV_WRAP	VideoCapture (const String &filename)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
CV_WRAP	VideoCapture (const String &filename, int apiPreference)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
CV_WRAP	VideoCapture (int index)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
virtual CV_WRAP bool	open (const String &filename)
	Open video file or a capturing device for video capturing.
virtual CV_WRAP bool	open (int index)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
virtual CV_WRAP bool	isOpened () const
	Returns true if video capturing has been initialized already.
virtual CV_WRAP void	release ()
	Closes video file or capturing device.
virtual CV_WRAP bool	grab ()
	Grabs the next frame from video file or capturing device.
virtual CV_WRAP bool	retrieve (OutputArray image, int flag=0)
	Decodes and returns the grabbed video frame.
virtual CV_WRAP bool	read (OutputArray image)
	Grabs, decodes and returns the next video frame.
virtual CV_WRAP bool	set (int propId, double value)
	Sets a property in the VideoCapture.
virtual CV_WRAP double	get (int propId) const
	Returns the specified VideoCapture property.
virtual CV_WRAP bool	open (const String &filename, int apiPreference)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Detailed Description

Class for video capturing from video files, image sequences or cameras.

The class provides C++ API for capturing video from cameras or for reading video files and image sequences. Here is how the class can be used: :

    #include "opencv2/opencv.hpp"

    using namespace cv;

    int main(int, char**)
    {
        VideoCapture  cap(0); // open the default camera
        if(!cap.isOpened())  // check if we succeeded
            return -1;

        Mat edges;
        namedWindow("edges",1);
        for(;;)
        {
            Mat frame;
            cap >> frame; // get a new frame from camera
            cvtColor(frame, edges, COLOR_BGR2GRAY);
            GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5);
            Canny(edges, edges, 0, 30, 3);
            imshow("edges", edges);
            if(waitKey(30) >= 0) break;
        }
        // the camera will be deinitialized automatically in VideoCapture destructor
        return 0;
    }

Note:

In C API the black-box structure CvCapture is used instead of VideoCapture.

A basic sample on using the VideoCapture interface can be found at opencv_source_code/samples/cpp/starter_video.cpp
Another basic video processing sample can be found at opencv_source_code/samples/cpp/video_dmtx.cpp
(Python) A basic sample on using the VideoCapture interface can be found at opencv_source_code/samples/python/video.py
(Python) Another basic video processing sample can be found at opencv_source_code/samples/python/video_dmtx.py
(Python) A multi threaded video processing sample can be found at opencv_source_code/samples/python/video_threaded.py

Definition at line 389 of file videoio.hpp.

Constructor & Destructor Documentation

CV_WRAP VideoCapture ( )

Note:: In C API, when you finished working with video, release CvCapture structure with cvReleaseCapture(), or use Ptr<CvCapture> that calls cvReleaseCapture() automatically in the destructor.

CV_WRAP VideoCapture ( const String & filename )

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 opened video file (eg. video.avi) or image sequence (eg. img_02d.jpg, which will read samples like img_00.jpg, img_01.jpg, img_02.jpg, ...)

CV_WRAP VideoCapture	(	const String &	filename,
		int	apiPreference
	)

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 opened video file (eg. video.avi) or image sequence (eg. img_02d.jpg, which will read samples like img_00.jpg, img_01.jpg, img_02.jpg, ...)
apiPreference	preferred Capture API to use. Can be used to enforce a specific reader implementation if multiple are available: e.g. CAP_FFMPEG or CAP_IMAGES

CV_WRAP VideoCapture ( int index )

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

Parameters:

index = camera_id + domain_offset (CAP_*). id of the video capturing device to open. If there is a single camera connected, just pass 0. Advanced Usage: to open Camera 1 using the MS Media Foundation API: index = 1 + CAP_MSMF

Member Function Documentation

virtual CV_WRAP double get ( int propId ) const [virtual]

Returns the specified VideoCapture property.

Parameters:

propId

Property identifier. It can be one of the following:

**CAP_PROP_POS_MSEC** Current position of the video file in milliseconds or video capture timestamp.
**CAP_PROP_POS_FRAMES** 0-based index of the frame to be decoded/captured next.
**CAP_PROP_POS_AVI_RATIO** Relative position of the video file: 0 - start of the film, 1 - end of the film.
**CAP_PROP_FRAME_WIDTH** Width of the frames in the video stream.
**CAP_PROP_FRAME_HEIGHT** Height of the frames in the video stream.
**CAP_PROP_FPS** Frame rate.
**CAP_PROP_FOURCC** 4-character code of codec.
**CAP_PROP_FRAME_COUNT** Number of frames in the video file.
**CAP_PROP_FORMAT** Format of the Mat objects returned by retrieve() .
**CAP_PROP_MODE** Backend-specific value indicating the current capture mode.
**CAP_PROP_BRIGHTNESS** Brightness of the image (only for cameras).
**CAP_PROP_CONTRAST** Contrast of the image (only for cameras).
**CAP_PROP_SATURATION** Saturation of the image (only for cameras).
**CAP_PROP_HUE** Hue of the image (only for cameras).
**CAP_PROP_GAIN** Gain of the image (only for cameras).
**CAP_PROP_EXPOSURE** Exposure (only for cameras).
**CAP_PROP_CONVERT_RGB** Boolean flags indicating whether images should be converted to RGB.
**CAP_PROP_WHITE_BALANCE** Currently not supported
**CAP_PROP_RECTIFICATION** Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently)

Note:: When querying a property that is not supported by the backend used by the VideoCapture class, value 0 is returned.

virtual CV_WRAP bool grab ( ) [virtual]

Grabs the next frame from video file or capturing device.

The methods/functions grab the next frame from video file or camera and return true (non-zero) in the case of success.

The primary use of the function is in multi-camera environments, especially when the cameras do not have hardware synchronization. That is, you call VideoCapture::grab() for each camera and after that call the slower method VideoCapture::retrieve() to decode and get frame from each camera. This way the overhead on demosaicing or motion jpeg decompression etc. is eliminated and the retrieved frames from different cameras will be closer in time.

Also, when a connected camera is multi-head (for example, a stereo camera or a Kinect device), the correct way of retrieving data from it is to call VideoCapture::grab first and then call VideoCapture::retrieve one or more times with different values of the channel parameter. See <https://github.com/Itseez/opencv/tree/master/samples/cpp/openni_capture.cpp>

virtual CV_WRAP bool isOpened ( ) const [virtual]

Returns true if video capturing has been initialized already.

If the previous call to VideoCapture constructor or VideoCapture::open succeeded, the method returns true.

virtual CV_WRAP bool open ( int index ) [virtual]

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

Parameters:

index = camera_id + domain_offset (CAP_*). id of the video capturing device to open. If there is a single camera connected, just pass 0. Advanced Usage: to open Camera 1 using the MS Media Foundation API: index = 1 + CAP_MSMF

virtual CV_WRAP bool open ( const String & filename ) [virtual]

Open video file or a capturing device for video capturing.

Parameters:

filename name of the opened video file (eg. video.avi) or image sequence (eg. img_02d.jpg, which will read samples like img_00.jpg, img_01.jpg, img_02.jpg, ...)

The methods first call VideoCapture::release to close the already opened file or camera.

virtual CV_WRAP bool open	(	const String &	filename,
		int	apiPreference
	)		`[virtual]`

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 opened video file (eg. video.avi) or image sequence (eg. img_02d.jpg, which will read samples like img_00.jpg, img_01.jpg, img_02.jpg, ...)
apiPreference	preferred Capture API to use. Can be used to enforce a specific reader implementation if multiple are available: e.g. CAP_FFMPEG or CAP_IMAGES

The methods first call VideoCapture::release to close the already opened file or camera.

virtual CV_WRAP bool read ( OutputArray image ) [virtual]

Grabs, decodes and returns the next video frame.

The methods/functions combine VideoCapture::grab and VideoCapture::retrieve in one call. This is the most convenient method for reading video files or capturing data from decode and return the just grabbed frame. If no frames has been grabbed (camera has been disconnected, or there are no more frames in video file), the methods return false and the functions return NULL pointer.

Note:: OpenCV 1.x functions cvRetrieveFrame and cv.RetrieveFrame return image stored inside the video capturing structure. It is not allowed to modify or release the image! You can copy the frame using :ocvcvCloneImage and then do whatever you want with the copy.

virtual CV_WRAP void release ( ) [virtual]

Closes video file or capturing device.

The methods are automatically called by subsequent VideoCapture::open and by VideoCapture destructor.

The C function also deallocates memory and clears \*capture pointer.

virtual CV_WRAP bool retrieve	(	OutputArray	image,
		int	flag = `0`
	)		`[virtual]`

Decodes and returns the grabbed video frame.

The methods/functions decode and return the just grabbed frame. If no frames has been grabbed (camera has been disconnected, or there are no more frames in video file), the methods return false and the functions return NULL pointer.

Note:: OpenCV 1.x functions cvRetrieveFrame and cv.RetrieveFrame return image stored inside the video capturing structure. It is not allowed to modify or release the image! You can copy the frame using :ocvcvCloneImage and then do whatever you want with the copy.

virtual CV_WRAP bool set	(	int	propId,
		double	value
	)		`[virtual]`

Sets a property in the VideoCapture.

Parameters:

propId

Property identifier. It can be one of the following:

**CAP_PROP_POS_MSEC** Current position of the video file in milliseconds.
**CAP_PROP_POS_FRAMES** 0-based index of the frame to be decoded/captured next.
**CAP_PROP_POS_AVI_RATIO** Relative position of the video file: 0 - start of the film, 1 - end of the film.
**CAP_PROP_FRAME_WIDTH** Width of the frames in the video stream.
**CAP_PROP_FRAME_HEIGHT** Height of the frames in the video stream.
**CAP_PROP_FPS** Frame rate.
**CAP_PROP_FOURCC** 4-character code of codec.
**CAP_PROP_FRAME_COUNT** Number of frames in the video file.
**CAP_PROP_FORMAT** Format of the Mat objects returned by retrieve() .
**CAP_PROP_MODE** Backend-specific value indicating the current capture mode.
**CAP_PROP_BRIGHTNESS** Brightness of the image (only for cameras).
**CAP_PROP_CONTRAST** Contrast of the image (only for cameras).
**CAP_PROP_SATURATION** Saturation of the image (only for cameras).
**CAP_PROP_HUE** Hue of the image (only for cameras).
**CAP_PROP_GAIN** Gain of the image (only for cameras).
**CAP_PROP_EXPOSURE** Exposure (only for cameras).
**CAP_PROP_CONVERT_RGB** Boolean flags indicating whether images should be converted to RGB.
**CAP_PROP_WHITE_BALANCE** Currently unsupported
**CAP_PROP_RECTIFICATION** Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently)

value Value of the property.

Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	31 Mar 2016
Imports:	152
Forks:	0
Commits:	1
Dependents:	0
Dependencies:	1
Followers:	2

VideoCapture Class Reference
[Media I/O]

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

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Repository details

Important Information for this Arm website

VideoCapture Class Reference [Media I/O]

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Repository toolbox

Repository details

Important Information for this Arm website

Access Warning

VideoCapture Class Reference
[Media I/O]