Package 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 Description
    protected long nativeObj  

  • Constructor Summary

    Constructors 
    Modifier Constructor 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
      VideoCapture​(int index, int apiPreference, MatOfInt params)
    Opens a camera for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...).
    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
      VideoCapture​(String filename, int apiPreference, MatOfInt params)
    Opens a video file or a capturing device or an IP video stream for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...).

  • Method Summary

    Modifier and Type Method 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​(int index, int apiPreference, MatOfInt params)
    Opens a camera for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...).
    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 open​(String filename, int apiPreference, MatOfInt params)
    Opens a video file or a capturing device or an IP video stream for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...).
    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 Details

  • Constructor Details

    • VideoCapture

      protected VideoCapture​(long addr)

    • 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.

    • 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)
      • 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: 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)
      • 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.
      implementation if multiple are available: e.g. cv::CAP_FFMPEG or cv::CAP_IMAGES or cv::CAP_DSHOW. SEE: cv::VideoCaptureAPIs

    • VideoCapture

      public VideoCapture​(String filename, int apiPreference, MatOfInt params)
      Opens a video file or a capturing device or an IP video stream for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...). See cv::VideoCaptureProperties
      Parameters:
      filename - automatically generated
      apiPreference - automatically generated
      params - 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_V4L. SEE: 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: cv::VideoCaptureAPIs

    • VideoCapture

      public VideoCapture​(int index, int apiPreference, MatOfInt params)
      Opens a camera for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...). See cv::VideoCaptureProperties
      Parameters:
      index - automatically generated
      apiPreference - automatically generated
      params - automatically generated

  • Method Details

    • getNativeObjAddr

      public long getNativeObjAddr()

    • __fromPtr__

      public static VideoCapture __fromPtr__​(long addr)

    • 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​(String filename, int apiPreference, MatOfInt params)
      Opens a video file or a capturing device or an IP video stream for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...). See cv::VideoCaptureProperties
      Parameters:
      filename - automatically generated
      apiPreference - automatically generated
      params - 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.

    • open

      public boolean open​(int index, int apiPreference, MatOfInt params)
      Opens a camera for video capturing with API Preference and parameters The params parameter allows to specify extra parameters encoded as pairs (paramId_1, paramValue_1, paramId_2, paramValue_2, ...). See cv::VideoCaptureProperties
      Parameters:
      index - automatically generated
      apiPreference - automatically generated
      params - 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.

    • 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

    • 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.

    • 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

    • 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.

    • 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.

    • 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

    • getBackendName

      public String getBackendName()
      Returns used backend API name Note: Stream should be opened.
      Returns:
      automatically generated

    • 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

    • getExceptionMode

      public boolean getExceptionMode()

    • finalize

      protected void finalize() throws Throwable
      Overrides:
      finalize in class Object
      Throws:
      Throwable