org.bytedeco.javacpp

Class opencv_videoio.VideoCapture

java.lang.Object

org.bytedeco.javacpp.Pointer

org.bytedeco.javacpp.opencv_videoio.VideoCapture

All Implemented Interfaces:

AutoCloseable

Enclosing class:

opencv_videoio

@Namespace(value="cv")
@NoOffset
public static class opencv_videoio.VideoCapture
extends Pointer

\brief 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.

\note - 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

Nested Class Summary

Nested classes/interfaces inherited from class org.bytedeco.javacpp.Pointer

Pointer.CustomDeallocator, Pointer.Deallocator, Pointer.NativeDeallocator

Field Summary

Fields inherited from class org.bytedeco.javacpp.Pointer

address, capacity, limit, position

Constructor Summary

Constructors

Constructor and Description
opencv_videoio.VideoCapture() \brief \note In C API, when you finished working with video, release CvCapture structure with cvReleaseCapture(), or use Ptr\ that calls cvReleaseCapture() automatically in the destructor.
opencv_videoio.VideoCapture(BytePointer filename) \overload
opencv_videoio.VideoCapture(BytePointer filename, int apiPreference) \overload
opencv_videoio.VideoCapture(int index) \overload
opencv_videoio.VideoCapture(long size) Native array allocator.
opencv_videoio.VideoCapture(Pointer p) Pointer cast constructor.
opencv_videoio.VideoCapture(String filename)
opencv_videoio.VideoCapture(String filename, int apiPreference)

Method Summary

Methods

Modifier and Type	Method and Description
double	get(int propId) \brief Returns the specified VideoCapture property
boolean	grab() \brief Grabs the next frame from video file or capturing device.
boolean	isOpened() \brief Returns true if video capturing has been initialized already.
boolean	open(BytePointer filename) \brief Open video file or a capturing device for video capturing
boolean	open(BytePointer filename, int apiPreference) \overload
boolean	open(int index) \overload
boolean	open(String filename)
boolean	open(String filename, int apiPreference)
opencv_videoio.VideoCapture	position(long position)
boolean	read(opencv_core.Mat image) \brief Grabs, decodes and returns the next video frame.
void	release() \brief Closes video file or capturing device.
boolean	retrieve(opencv_core.Mat image)
boolean	retrieve(opencv_core.Mat image, int flag) \brief Decodes and returns the grabbed video frame.
boolean	set(int propId, double value) \brief Sets a property in the VideoCapture.
opencv_videoio.VideoCapture	shiftRight(opencv_core.Mat image)
opencv_videoio.VideoCapture	shiftRight(opencv_core.UMat image)

Methods inherited from class org.bytedeco.javacpp.Pointer

address, asBuffer, asByteBuffer, capacity, capacity, close, deallocate, deallocate, deallocateReferences, deallocator, deallocator, equals, fill, hashCode, isNull, limit, limit, maxBytes, memchr, memcmp, memcpy, memmove, memset, offsetof, position, put, setNull, sizeof, toString, totalBytes, withDeallocator, zero

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(Pointer p)

Pointer cast constructor. Invokes Pointer.Pointer(Pointer).

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(long size)

Native array allocator. Access with Pointer.position(long).

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture()

\brief \note In C API, when you finished working with video, release CvCapture structure with cvReleaseCapture(), or use Ptr\ that calls cvReleaseCapture() automatically in the destructor.

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(@opencv_core.Str
                           BytePointer filename)

\overload

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, ...)

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(@opencv_core.Str
                           String filename)

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(@opencv_core.Str
                           BytePointer filename,
                           int apiPreference)

\overload

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

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(@opencv_core.Str
                           String filename,
                           int apiPreference)

opencv_videoio.VideoCapture

public opencv_videoio.VideoCapture(int index)

\overload

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

Method Detail

position

public opencv_videoio.VideoCapture position(long position)

Overrides:

position in class Pointer

open

@Cast(value="bool")
public boolean open(@opencv_core.Str
                     BytePointer filename)

\brief 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.

open

@Cast(value="bool")
public boolean open(@opencv_core.Str
                     String filename)

open

@Cast(value="bool")
public boolean open(int index)

\overload

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

isOpened

@Cast(value="bool")
public boolean isOpened()

\brief Returns true if video capturing has been initialized already.

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

release

public void release()

\brief 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.

grab

@Cast(value="bool")
public boolean grab()

\brief 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

retrieve

@Cast(value="bool")
public boolean retrieve(@ByVal
                         opencv_core.Mat image,
                         int flag)

\brief 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.

retrieve

@Cast(value="bool")
public boolean retrieve(@ByVal
                         opencv_core.Mat image)

shiftRight

@ByRef
@Name(value="operator >>")
public opencv_videoio.VideoCapture shiftRight(@ByRef
                                                     opencv_core.Mat image)

shiftRight

@ByRef
@Name(value="operator >>")
public opencv_videoio.VideoCapture shiftRight(@ByRef
                                                     opencv_core.UMat image)

read

@Cast(value="bool")
public boolean read(@ByVal
                     opencv_core.Mat image)

\brief 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.

set

@Cast(value="bool")
public boolean set(int propId,
                    double value)

\brief 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.

get

public double get(int propId)

\brief 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.

open

@Cast(value="bool")
public boolean open(@opencv_core.Str
                     BytePointer filename,
                     int apiPreference)

\overload

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.

open

@Cast(value="bool")
public boolean open(@opencv_core.Str
                     String filename,
                     int apiPreference)