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 org.bytedeco.javacpp.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 samples/cpp/videocapture_basic.cpp

\note In \ref videoio_c "C API" the black-box structure CvCapture is used instead of %VideoCapture. \note - (C++) A basic sample on using the %VideoCapture interface can be found at OPENCV_SOURCE_CODE/samples/cpp/videocapture_starter.cpp - (Python) A basic sample on using the %VideoCapture interface can be found at OPENCV_SOURCE_CODE/samples/python/video.py - (Python) A multi threaded video processing sample can be found at OPENCV_SOURCE_CODE/samples/python/video_threaded.py - (Python) %VideoCapture sample showcasing some features of the Video4Linux2 backend OPENCV_SOURCE_CODE/samples/python/video_v4l2.py

Nested Class Summary

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

org.bytedeco.javacpp.Pointer.CustomDeallocator, org.bytedeco.javacpp.Pointer.Deallocator, org.bytedeco.javacpp.Pointer.NativeDeallocator

Field Summary

Fields inherited from class org.bytedeco.javacpp.Pointer

address, capacity, limit, position

Constructor Summary

Constructors

Constructor and Description
VideoCapture() \brief Default constructor \note In \ref videoio_c "C API", when you finished working with video, release CvCapture structure with cvReleaseCapture(), or use Ptr\ that calls cvReleaseCapture() automatically in the destructor.
VideoCapture(org.bytedeco.javacpp.BytePointer filename) \overload \brief Open video file or a capturing device or a IP video stream for video capturing
VideoCapture(org.bytedeco.javacpp.BytePointer filename, int apiPreference) \overload \brief Open video file or a capturing device or a IP video stream for video capturing with API Preference
VideoCapture(int index) \overload \brief Open a camera for video capturing
VideoCapture(long size) Native array allocator.
VideoCapture(org.bytedeco.javacpp.Pointer p) Pointer cast constructor.
VideoCapture(String filename)
VideoCapture(String filename, int apiPreference)

Method Summary

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(org.bytedeco.javacpp.BytePointer filename) \brief Open video file or a capturing device or a IP video stream for video capturing
boolean	open(org.bytedeco.javacpp.BytePointer filename, int apiPreference) \brief Open video file or a capturing device or a IP video stream for video capturing with API Preference
boolean	open(int index) \brief Open a camera for video capturing
boolean	open(int cameraNum, int apiPreference) \brief Open a camera for video capturing
boolean	open(String filename)
boolean	open(String filename, int apiPreference)
opencv_videoio.VideoCapture	position(long position)
boolean	read(opencv_core.GpuMat image)
boolean	read(opencv_core.Mat image) \brief Grabs, decodes and returns the next video frame.
boolean	read(opencv_core.UMat image)
void	release() \brief Closes video file or capturing device.
boolean	retrieve(opencv_core.GpuMat image)
boolean	retrieve(opencv_core.GpuMat image, int flag)
boolean	retrieve(opencv_core.Mat image)
boolean	retrieve(opencv_core.Mat image, int flag) \brief Decodes and returns the grabbed video frame.
boolean	retrieve(opencv_core.UMat image)
boolean	retrieve(opencv_core.UMat image, int flag)
boolean	set(int propId, double value) \brief Sets a property in the VideoCapture.
opencv_videoio.VideoCapture	shiftRight(opencv_core.Mat image) \brief Stream operator to read the next video frame.
opencv_videoio.VideoCapture	shiftRight(opencv_core.UMat image) \overload \sa read()

Methods inherited from class org.bytedeco.javacpp.Pointer

address, asBuffer, asByteBuffer, availablePhysicalBytes, calloc, capacity, capacity, close, deallocate, deallocate, deallocateReferences, deallocator, deallocator, equals, fill, formatBytes, free, hashCode, isNull, limit, limit, malloc, maxBytes, maxPhysicalBytes, memchr, memcmp, memcpy, memmove, memset, offsetof, parseBytes, physicalBytes, position, put, realloc, setNull, sizeof, toString, totalBytes, totalPhysicalBytes, withDeallocator, zero

Methods inherited from class java.lang.Object

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

Constructor Detail

VideoCapture

public VideoCapture(org.bytedeco.javacpp.Pointer p)

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

VideoCapture

public VideoCapture(long size)

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

VideoCapture

public VideoCapture()

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

VideoCapture

public VideoCapture(@opencv_core.Str
                    org.bytedeco.javacpp.BytePointer filename)

\overload \brief Open video file or a capturing device or a IP video stream for video capturing

Same as VideoCapture(const String& filename, int apiPreference) but using default Capture API backends

VideoCapture

public VideoCapture(@opencv_core.Str
                    String filename)

VideoCapture

public VideoCapture(@opencv_core.Str
                    org.bytedeco.javacpp.BytePointer filename,
                    int apiPreference)

\overload \brief Open video file or a capturing device or a IP video stream for video capturing with API Preference

Parameters:

filename - it can be: - name of 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, ...) - or URL of video stream (eg. protocol://host:port/script_name?script_params|auth). Note that each video stream or IP camera feed has its own URL scheme. Please refer to the documentation of source stream to know the right URL.

apiPreference - preferred Capture 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_IMAGES or cv::CAP_DSHOW. \sa The list of supported API backends cv::VideoCaptureAPIs

VideoCapture

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

VideoCapture

public VideoCapture(int index)

\overload \brief Open a camera for video capturing

Parameters:

index - camera_id + domain_offset (CAP_*) id of the video capturing device to open. To open default camera using default backend just pass 0. Use a domain_offset to enforce a specific reader implementation if multiple are available like cv::CAP_FFMPEG or cv::CAP_IMAGES or cv::CAP_DSHOW. e.g. to open Camera 1 using the MS Media Foundation API use index = 1 + cv::CAP_MSMF

\sa The list of supported API backends cv::VideoCaptureAPIs

Method Detail

position

public opencv_videoio.VideoCapture position(long position)

Overrides:

position in class org.bytedeco.javacpp.Pointer

open

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

\brief Open video file or a capturing device or a IP video stream for video capturing

\overload

Parameters are same as the constructor VideoCapture(const String& filename)

Returns:

true if the file has been successfully opened

The method first calls 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)

\brief Open a camera for video capturing

\overload

Parameters are same as the constructor VideoCapture(int index)

Returns:

true if the camera has been successfully opened.

The method first calls VideoCapture::release to close the already opened file or camera.

open

@Cast(value="bool")
public boolean open(int cameraNum,
                                        int apiPreference)

\brief Open a camera for video capturing

\overload

Parameters are similar as the constructor VideoCapture(int index),except it takes an additional argument apiPreference. Definitely, is same as open(int index) where index=cameraNum + apiPreference

Returns:

true if the camera has been successfully opened.

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 method is 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.

Returns:

true (non-zero) in the case of success.

The method/function grabs the next frame from video file or camera and returns 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.

\ref tutorial_kinect_openni

retrieve

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

\brief Decodes and returns the grabbed video frame.

Parameters:

[out] - image the video frame is returned here. If no frames has been grabbed the image will be empty.

flag - it could be a frame index or a driver specific flag

Returns:

false if no frames has been grabbed

The method decodes and returns the just grabbed frame. If no frames has been grabbed (camera has been disconnected, or there are no more frames in video file), the method returns false and the function returns an empty image (with %cv::Mat, test it with Mat::empty()).

\sa read()

\note In \ref videoio_c "C API", 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)

retrieve

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

retrieve

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

retrieve

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

retrieve

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

shiftRight

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

\brief Stream operator to read the next video frame. \sa read()

shiftRight

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

\overload \sa read()

read

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

\brief Grabs, decodes and returns the next video frame.

Parameters:

[out] - image the video frame is returned here. If no frames has been grabbed the image will be empty.

Returns:

false if no frames has been grabbed

The method/function combines VideoCapture::grab() and VideoCapture::retrieve() in one call. This is the most convenient method for reading video files or capturing data from decode and returns the just grabbed frame. If no frames has been grabbed (camera has been disconnected, or there are no more frames in video file), the method returns false and the function returns empty image (with %cv::Mat, test it with Mat::empty()).

\note In \ref videoio_c "C API", 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.

read

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

read

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

set

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

\brief Sets a property in the VideoCapture.

Parameters:

propId - Property identifier from cv::VideoCaptureProperties (eg. cv::CAP_PROP_POS_MSEC, cv::CAP_PROP_POS_FRAMES, ...) or one from \ref videoio_flags_others

value - Value of the property.

Returns:

true if the property is supported by backend used by the VideoCapture instance. \note Even if it returns true this doesn't ensure that the property value has been accepted by the capture device. See note in VideoCapture::get()

get

public double get(int propId)

\brief Returns the specified VideoCapture property

Parameters:

propId - Property identifier from cv::VideoCaptureProperties (eg. cv::CAP_PROP_POS_MSEC, cv::CAP_PROP_POS_FRAMES, ...) or one from \ref videoio_flags_others

Returns:

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

\note Reading / writing properties involves many layers. Some unexpected result might happens along this chain.

 {.txt}
    `VideoCapture -> API Backend -> Operating System -> Device Driver -> Device Hardware`
    

The returned value might be different from what really used by the device or it could be encoded using device dependent rules (eg. steps or percentage). Effective behaviour depends from device driver and API Backend

open

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

\brief Open video file or a capturing device or a IP video stream for video capturing with API Preference

\overload

Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference)

Returns:

true if the file has been successfully opened

The method first calls VideoCapture::release to close the already opened file or camera.

open

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