Package org.opencv.videoio
Class VideoCapture
- java.lang.Object
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- org.opencv.videoio.VideoCapture
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public class VideoCapture extends java.lang.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/snippets/videocapture_basic.cpp Note:-
(C++) A basic sample on using the %VideoCapture interface can be found at
OPENCV_SOURCE_CODE/samples/cpp/videocapture_combined.cpp
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(Python) A basic sample on using the %VideoCapture interface can be found at
OPENCV_SOURCE_CODE/samples/python/video.py
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(Python) A multi threaded video processing sample can be found at
OPENCV_SOURCE_CODE/samples/python/video_threaded.py
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(Python) %VideoCapture sample showcasing some features of the Video4Linux2 backend
OPENCV_SOURCE_CODE/samples/python/video_v4l2.py
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(C++) A basic sample on using the %VideoCapture interface can be found at
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Field Summary
Fields Modifier and Type Field Description protected long
nativeObj
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Constructor Summary
Constructors Modifier Constructor Description VideoCapture()
Default constructorVideoCapture(int index)
Opens a camera for video capturingVideoCapture(int index, int apiPreference)
Opens a camera for video capturingVideoCapture(int index, int apiPreference, MatOfInt params)
Opens a camera for video capturing with API Preference and parameters Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
.protected
VideoCapture(long addr)
VideoCapture(java.lang.String filename)
Opens a video file or a capturing device or an IP video stream for video capturing with API PreferenceVideoCapture(java.lang.String filename, int apiPreference)
Opens a video file or a capturing device or an IP video stream for video capturing with API PreferenceVideoCapture(java.lang.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 Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description static VideoCapture
__fromPtr__(long addr)
protected void
finalize()
double
get(int propId)
Returns the specified VideoCapture propertyjava.lang.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 Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
.boolean
open(java.lang.String filename)
Opens a video file or a capturing device or an IP video stream for video capturing.boolean
open(java.lang.String filename, int apiPreference)
Opens a video file or a capturing device or an IP video stream for video capturing.boolean
open(java.lang.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 Theparams
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
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Constructor Detail
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VideoCapture
protected VideoCapture(long addr)
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VideoCapture
public VideoCapture()
Default constructor
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VideoCapture
public VideoCapture(java.lang.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 likeimg_00.jpg, img_01.jpg, img_02.jpg, ...
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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.
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name of video file (eg.
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
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VideoCapture
public VideoCapture(java.lang.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 likeimg_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.
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name of video file (eg.
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VideoCapture
public VideoCapture(java.lang.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 Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
. See cv::VideoCaptureProperties- Parameters:
filename
- automatically generatedapiPreference
- automatically generatedparams
- automatically generated
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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
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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
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VideoCapture
public VideoCapture(int index, int apiPreference, MatOfInt params)
Opens a camera for video capturing with API Preference and parameters Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
. See cv::VideoCaptureProperties- Parameters:
index
- automatically generatedapiPreference
- automatically generatedparams
- automatically generated
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Method Detail
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getNativeObjAddr
public long getNativeObjAddr()
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__fromPtr__
public static VideoCapture __fromPtr__(long addr)
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open
public boolean open(java.lang.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 generatedapiPreference
- 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.
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open
public boolean open(java.lang.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.
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open
public boolean open(java.lang.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 Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
. See cv::VideoCaptureProperties- Parameters:
filename
- automatically generatedapiPreference
- automatically generatedparams
- 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.
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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 generatedapiPreference
- 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.
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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.
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open
public boolean open(int index, int apiPreference, MatOfInt params)
Opens a camera for video capturing with API Preference and parameters Theparams
parameter allows to specify extra parameters encoded as pairs(paramId_1, paramValue_1, paramId_2, paramValue_2, ...)
. See cv::VideoCaptureProperties- Parameters:
index
- automatically generatedapiPreference
- automatically generatedparams
- 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.
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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
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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.
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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
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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 flagimage
- 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()
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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()
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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()).
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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_othersvalue
- Value of the property.- Returns:
true
if the property is supported by backend used by the VideoCapture instance. Note: Even if it returnstrue
this doesn't ensure that the property value has been accepted by the capture device. See note in VideoCapture::get()
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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
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getBackendName
public java.lang.String getBackendName()
Returns used backend API name Note: Stream should be opened.- Returns:
- automatically generated
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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
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getExceptionMode
public boolean getExceptionMode()
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finalize
protected void finalize() throws java.lang.Throwable
- Overrides:
finalize
in classjava.lang.Object
- Throws:
java.lang.Throwable
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