org.bytedeco.opencv.opencv_videoio

Class VideoCapture

java.lang.Object

org.bytedeco.javacpp.Pointer

org.bytedeco.opencv.opencv_videoio.VideoCapture

All Implemented Interfaces:

AutoCloseable

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

\endcond IGNORED

/** \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

Pointer.CustomDeallocator, Pointer.Deallocator, Pointer.NativeDeallocator, Pointer.ReferenceCounter

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(BytePointer filename)
VideoCapture(BytePointer filename, int apiPreference) \overload \brief Opens a video file or a capturing device or an IP video stream for video capturing with API Preference
VideoCapture(int index)
VideoCapture(int index, int apiPreference) \overload \brief Opens a camera for video capturing
VideoCapture(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
BytePointer	getBackendName() \brief Returns used backend API name
boolean	getExceptionMode() query if exception mode is active
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)
boolean	open(BytePointer filename, int apiPreference) \brief Opens a video file or a capturing device or an IP video stream for video capturing.
boolean	open(int index)
boolean	open(int index, int apiPreference) \brief Opens a camera for video capturing
boolean	open(String filename)
boolean	open(String filename, int apiPreference)
boolean	read(GpuMat image)
boolean	read(Mat image) \brief Grabs, decodes and returns the next video frame.
boolean	read(UMat image)
void	release() \brief Closes video file or capturing device.
boolean	retrieve(GpuMat image)
boolean	retrieve(GpuMat image, int flag)
boolean	retrieve(Mat image)
boolean	retrieve(Mat image, int flag) \brief Decodes and returns the grabbed video frame.
boolean	retrieve(UMat image)
boolean	retrieve(UMat image, int flag)
boolean	set(int propId, double value) \brief Sets a property in the VideoCapture.
void	setExceptionMode(boolean enable) Switches exceptions mode methods raise exceptions if not successful instead of returning an error code
VideoCapture	shiftRight(Mat image) \brief Stream operator to read the next video frame.
VideoCapture	shiftRight(UMat image) \overload
static boolean	waitAny(VideoCapture streams, int[] readyIndex)
static boolean	waitAny(VideoCapture streams, int[] readyIndex, long timeoutNs)
static boolean	waitAny(VideoCapture streams, IntBuffer readyIndex)
static boolean	waitAny(VideoCapture streams, IntBuffer readyIndex, long timeoutNs)
static boolean	waitAny(VideoCapture streams, IntPointer readyIndex)
static boolean	waitAny(VideoCapture streams, IntPointer readyIndex, long timeoutNs) \brief Wait for ready frames from VideoCapture.

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, isNull, limit, limit, malloc, maxBytes, maxPhysicalBytes, memchr, memcmp, memcpy, memmove, memset, offsetof, parseBytes, physicalBytes, position, position, put, realloc, referenceCount, releaseReference, retainReference, 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(Pointer p)

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

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
                    BytePointer filename,
                    int apiPreference)

\overload \brief Opens a video file or a capturing device or an 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) - or GStreamer pipeline string in gst-launch tool format in case if GStreamer is used as backend 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.

See Also:

cv::VideoCaptureAPIs

VideoCapture

public VideoCapture(@opencv_core.Str
                    BytePointer filename)

VideoCapture

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

VideoCapture

public VideoCapture(@opencv_core.Str
                    String filename)

VideoCapture

public VideoCapture(int index,
                    int apiPreference)

\overload \brief Opens a camera for video capturing

Parameters:

index - id of the video capturing device to open. To open default camera using default backend just pass 0. (to backward compatibility usage of camera_id + domain_offset (CAP_*) is valid when apiPreference is CAP_ANY)

apiPreference - preferred Capture API backends to use. Can be used to enforce a specific reader implementation if multiple are available: e.g. cv::CAP_DSHOW or cv::CAP_MSMF or cv::CAP_V4L.

See Also:

cv::VideoCaptureAPIs

VideoCapture

public VideoCapture(int index)

Method Detail

open

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

\brief Opens a video file or a capturing device or an IP video stream for video capturing.

\overload

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

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
                                        BytePointer filename)

open

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

open

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

open

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

\brief Opens a camera for video capturing

\overload

Parameters are same as the constructor VideoCapture(int index, int apiPreference = CAP_ANY)

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 index)

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
                                            Mat image,
                                            int flag)

\brief Decodes and returns the grabbed video frame.

Parameters:

image - [out] 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()).

See Also:

\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 cvCloneImage and then do whatever you want with the copy.

retrieve

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

retrieve

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

retrieve

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

retrieve

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

retrieve

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

shiftRight

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

\brief Stream operator to read the next video frame.

See Also:

read()

shiftRight

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

\overload

See Also:

read()

read

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

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

Parameters:

image - [out] 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 cvCloneImage and then do whatever you want with the copy.

read

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

read

@Cast(value="bool")
public boolean read(@ByVal
                                        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

getBackendName

@opencv_core.Str
public BytePointer getBackendName()

\brief Returns used backend API name

\note Stream should be opened.

setExceptionMode

public void setExceptionMode(@Cast(value="bool")
                             boolean enable)

Switches exceptions mode methods raise exceptions if not successful instead of returning an error code

getExceptionMode

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

query if exception mode is active

waitAny

@Cast(value="bool")
public static boolean waitAny(@StdVector
                                                  VideoCapture streams,
                                                  @StdVector
                                                  IntPointer readyIndex,
                                                  @Cast(value="int64")
                                                  long timeoutNs)

\brief Wait for ready frames from VideoCapture.

Parameters:

streams - input video streams

readyIndex - stream indexes with grabbed frames (ready to use .retrieve() to fetch actual frame)

timeoutNs - number of nanoseconds (0 - infinite)

Returns:

true if streamReady is not empty

Throws:

Exception - %Exception on stream errors (check .isOpened() to filter out malformed streams) or VideoCapture type is not supported

The primary use of the function is in multi-camera environments. The method fills the ready state vector, grabbs video frame, if camera is ready.

After this call use VideoCapture::retrieve() to decode and fetch frame data.

waitAny

@Cast(value="bool")
public static boolean waitAny(@StdVector
                                                  VideoCapture streams,
                                                  @StdVector
                                                  IntPointer readyIndex)

waitAny

@Cast(value="bool")
public static boolean waitAny(@StdVector
                                                  VideoCapture streams,
                                                  @StdVector
                                                  IntBuffer readyIndex,
                                                  @Cast(value="int64")
                                                  long timeoutNs)

waitAny

@Cast(value="bool")
public static boolean waitAny(@StdVector
                                                  VideoCapture streams,
                                                  @StdVector
                                                  IntBuffer readyIndex)

waitAny

@Cast(value="bool")
public static boolean waitAny(@StdVector
                                                  VideoCapture streams,
                                                  @StdVector
                                                  int[] readyIndex,
                                                  @Cast(value="int64")
                                                  long timeoutNs)

waitAny

@Cast(value="bool")
public static boolean waitAny(@StdVector
                                                  VideoCapture streams,
                                                  @StdVector
                                                  int[] readyIndex)