VideoCapture (OpenCV 4.1.2 Java documentation)

java.lang.Object
- org.opencv.videoio.VideoCapture

```
public class VideoCapture
extends Object
```
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

Field Summary

Fields
Modifier and Type Field and Description

protected long nativeObj

Fields
Modifier and Type	Field and Description
`protected long`	`nativeObj`

Constructor Summary

Constructors
Modifier	Constructor and Description
	`VideoCapture()` Default constructor Note: In REF: videoio_c "C API", when you finished working with video, release CvCapture structure with cvReleaseCapture(), or use Ptr<CvCapture> that calls cvReleaseCapture() automatically in the destructor.
	`VideoCapture(int index)` Opens a camera for video capturing
	`VideoCapture(int index, int apiPreference)` Opens a camera for video capturing
`protected`	`VideoCapture(long addr)`
	`VideoCapture(String filename)` Opens a video file or a capturing device or an IP video stream for video capturing with API Preference
	`VideoCapture(String filename, int apiPreference)` Opens a video file or a capturing device or an IP video stream for video capturing with API Preference

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`static VideoCapture`	`__fromPtr__(long addr)`
`protected void`	`finalize()`
`double`	`get(int propId)` Returns the specified VideoCapture property
`String`	`getBackendName()` Returns used backend API name Note: Stream should be opened.
`boolean`	`getExceptionMode()`
`long`	`getNativeObjAddr()`
`boolean`	`grab()` Grabs the next frame from video file or capturing device.
`boolean`	`isOpened()` Returns true if video capturing has been initialized already.
`boolean`	`open(int index)` Opens a camera for video capturing Parameters are same as the constructor VideoCapture(int index, int apiPreference = CAP_ANY)
`boolean`	`open(int index, int apiPreference)` Opens a camera for video capturing Parameters are same as the constructor VideoCapture(int index, int apiPreference = CAP_ANY)
`boolean`	`open(String filename)` Opens a video file or a capturing device or an IP video stream for video capturing.
`boolean`	`open(String filename, int apiPreference)` Opens a video file or a capturing device or an IP video stream for video capturing.
`boolean`	`read(Mat image)` Grabs, decodes and returns the next video frame.
`void`	`release()` Closes video file or capturing device.
`boolean`	`retrieve(Mat image)` Decodes and returns the grabbed video frame.
`boolean`	`retrieve(Mat image, int flag)` Decodes and returns the grabbed video frame.
`boolean`	`set(int propId, double value)` 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

Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - nativeObj
```
protected final long nativeObj
```
- Constructor Detail
  - VideoCapture
```
protected VideoCapture(long addr)
```
  - VideoCapture
```
public VideoCapture(String filename,
                    int apiPreference)
```
    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). 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: The list of supported API backends cv::VideoCaptureAPIs
- VideoCapture
```
public VideoCapture(String filename)
```
  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). 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. implementation if multiple are available: e.g. cv::CAP_FFMPEG or cv::CAP_IMAGES or cv::CAP_DSHOW. SEE: The list of supported API backends cv::VideoCaptureAPIs
- VideoCapture
```
public VideoCapture(int index,
                    int apiPreference)
```
  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: The list of supported API backends cv::VideoCaptureAPIs
- VideoCapture
```
public VideoCapture(int index)
```
  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) implementation if multiple are available: e.g. cv::CAP_DSHOW or cv::CAP_MSMF or cv::CAP_V4L. SEE: The list of supported API backends cv::VideoCaptureAPIs
- VideoCapture
```
public VideoCapture()
```
  Default constructor Note: In REF: videoio_c "C API", when you finished working with video, release CvCapture structure with cvReleaseCapture(), or use Ptr<CvCapture> that calls cvReleaseCapture() automatically in the destructor.

Method Detail
- getNativeObjAddr
```
public long getNativeObjAddr()
```
- __fromPtr__
```
public static VideoCapture __fromPtr__(long addr)
```
- getBackendName
```
public String getBackendName()
```
  Returns used backend API name Note: Stream should be opened.
  
  Returns:
  
  automatically generated
- getExceptionMode
```
public boolean getExceptionMode()
```
- grab
```
public boolean grab()
```
  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
- isOpened
```
public boolean isOpened()
```
  Returns true if video capturing has been initialized already. If the previous call to VideoCapture constructor or VideoCapture::open() succeeded, the method returns true.
  
  Returns:
  
  automatically generated
- open
```
public boolean open(String filename,
                    int apiPreference)
```
  Opens a video file or a capturing device or an IP video stream for video capturing. Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference = CAP_ANY)
  
  Parameters:
  
  filename - automatically generated
  
  apiPreference - automatically generated
  
  Returns:
  
  true if the file has been successfully opened The method first calls VideoCapture::release to close the already opened file or camera.
- open
```
public boolean open(String filename)
```
  Opens a video file or a capturing device or an IP video stream for video capturing. Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference = CAP_ANY)
  
  Parameters:
  
  filename - automatically generated
  
  Returns:
  
  true if the file has been successfully opened The method first calls VideoCapture::release to close the already opened file or camera.
- open
```
public boolean open(int index,
                    int apiPreference)
```
  Opens a camera for video capturing Parameters are same as the constructor VideoCapture(int index, int apiPreference = CAP_ANY)
  
  Parameters:
  
  index - automatically generated
  
  apiPreference - automatically generated
  
  Returns:
  
  true if the camera has been successfully opened. The method first calls VideoCapture::release to close the already opened file or camera.
- open
```
public boolean open(int index)
```
  Opens a camera for video capturing Parameters are same as the constructor VideoCapture(int index, int apiPreference = CAP_ANY)
  
  Parameters:
  
  index - automatically generated
  
  Returns:
  
  true if the camera has been successfully opened. The method first calls VideoCapture::release to close the already opened file or camera.
- read
```
public boolean read(Mat image)
```
  Grabs, decodes and returns the next video frame.
  
  Parameters:
  
  image - automatically generated
  
  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.
- retrieve
```
public boolean retrieve(Mat image,
                        int flag)
```
  Decodes and returns the grabbed video frame.
  
  Parameters:
  
  flag - it could be a frame index or a driver specific flag
  
  image - automatically generated
  
  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: 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 cvCloneImage and then do whatever you want with the copy.
- retrieve
```
public boolean retrieve(Mat image)
```
  Decodes and returns the grabbed video frame.
  
  Parameters:
  
  image - automatically generated
  
  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: 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 cvCloneImage and then do whatever you want with the copy.
- set
```
public boolean set(int propId,
                   double value)
```
  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)
```
  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. 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
- release
```
public void release()
```
  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.
- setExceptionMode
```
public void setExceptionMode(boolean enable)
```
  Switches exceptions mode methods raise exceptions if not successful instead of returning an error code
  
  Parameters:
  
  enable - automatically generated
- finalize
```
protected void finalize()
                 throws Throwable
```
  Overrides:
  
  finalize in class Object
  
  Throws:
  
  Throwable

Class VideoCapture

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

nativeObj

Constructor Detail

VideoCapture

VideoCapture

VideoCapture

VideoCapture

VideoCapture

VideoCapture

Method Detail

getNativeObjAddr

__fromPtr__

getBackendName

getExceptionMode

grab

isOpened

open

open

open

open

read

retrieve

retrieve

set

get

release

setExceptionMode

finalize

fromPtr