org.opencv.videoio

## Class VideoCapture

- 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`

  - ### 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)` Open a camera for video capturing
    `` | `VideoCapture(int index, int apiPreference)` Opens a camera for video capturing
    `protected` | `VideoCapture(long addr)`
    `` | `VideoCapture(String filename)` 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(String filename, int apiPreference)` Open video file or a capturing device or a 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.
    `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)` Open a camera for video capturing Parameters are same as the constructor VideoCapture(int index)
    `boolean` | `open(int cameraNum, int apiPreference)` Open a camera for video capturing Parameters are similar as the constructor VideoCapture(int index),except it takes an additional argument apiPreference.
    `boolean` | `open(String filename)` Open video file or a capturing device or a IP video stream for video capturing Parameters are same as the constructor VideoCapture(const String& filename)
    `boolean` | `open(String filename, int apiPreference)` Open video file or a capturing device or a IP video stream for video capturing with API Preference Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference)
    `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.

    - ### 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)

      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. SEE: The list of supported API backends cv::VideoCaptureAPIs

  - #### VideoCapture

        public VideoCapture(String filename)

    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
    Parameters:
      `filename` - automatically generated

  - #### 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_V4L2. SEE: The list of supported API backends cv::VideoCaptureAPIs

  - #### VideoCapture

        public VideoCapture(int index)

    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` 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

  - #### 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)

    Open video file or a capturing device or a IP video stream for video capturing with API Preference Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference)
    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)

    Open video file or a capturing device or a IP video stream for video capturing Parameters are same as the constructor VideoCapture(const String& filename)
    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 cameraNum,
                            int apiPreference)

    Open a camera for video capturing 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`
    Parameters:
      `cameraNum` - automatically generated
      `apiPreference` - automatically generated
    Returns:
      `true` if the camera has been successfully opened.

  - #### open

        public boolean open(int index)

    Open a camera for video capturing Parameters are same as the constructor VideoCapture(int index)
    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.

  - #### finalize

        protected void finalize()
                         throws Throwable

    Overrides:
      `finalize` in class `Object`
    Throws:
      `Throwable`

Generated on Wed Oct 9 2019 16:55:37 UTC / OpenCV 3.4.8