classdef VideoCapture < handle %VIDEOCAPTURE VideoCapture wrapper class % % Class for video capturing from video files or cameras. The class % provides Matlab API for capturing video from cameras or for reading % video files. Here is how the class can be used: % % cap = cv.VideoCapture; % pause(3); % Note below % for t = 1:30 % imshow(cap.read); % pause(0.1); % end % % ## Note % In some environment, there is a concurrency issue during camera % initialization. To avoid unexpected crash, pause for seconds after % the initialization of VideoCapture object. % % See also cv.VideoCapture.VideoCapture cv.VideoCapture.read % cv.VideoCapture.get cv.VideoCapture.set % properties (SetAccess = private) % Object ID id end methods function this = VideoCapture(filename) %VIDEOCAPTURE Create a new VideoCapture object % % cap = cv.VideoCapture % cap = cv.VideoCapture(devid) % cap = cv.VideoCapture(filename) % % VideoCapture create a new instance. With no argument, it % connects to the default camera device found in the system. % You can specify camera devices by devid, an integer value % starting from 0. You can also specify a filename to open a % video file. % % See also cv.VideoCapture % if nargin < 1, filename = 0; end this.id = VideoCapture_(filename); end function delete(this) %DELETE Destructor of VideoCapture object VideoCapture_(this.id, 'delete'); end function frame = read(this) %READ Grabs, decodes and returns the next video frame % % frame = cap.read() % % The method captures the next video frame and return it. If % capturing fails, empty array will be returned instead. % % See also cv.VideoCapture % frame = VideoCapture_(this.id, 'read'); end function value = get(this, key) %GET Returns the specified VideoCapture property % % value = cap.get(PropertyName) % % The method returns a Property value of VideoCapture. % PropertyName can be one of the followings: % % 'PosMsec' Current position of the video file in milliseconds or video capture timestamp. % 'PosFrames' 0-based index of the frame to be decoded/captured next. % 'AVIRatio' Relative position of the video file: 0 - start of the film, 1 - end of the film. % 'FrameWidth' Width of the frames in the video stream. % 'FrameHeight' Height of the frames in the video stream. % 'FPS' Frame rate. % 'FourCC' 4-character code of codec. % 'FrameCount' Number of frames in the video file. % 'Format' Format of the Mat objects returned by retrieve() . % 'Mode' Backend-specific value indicating the current capture mode. % 'Brightness' Brightness of the image (only for cameras). % 'Contrast' Contrast of the image (only for cameras). % 'Saturation' Saturation of the image (only for cameras). % 'Hue' Hue of the image (only for cameras). % 'Gain' Gain of the image (only for cameras). % 'Exposure' Exposure (only for cameras). % 'ConvertRGB' Boolean flags indicating whether images should be converted to RGB. % 'Rectification' Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently) % % See also cv.VideoCapture % value = VideoCapture_(this.id, 'get', key); end function set(this, key, value) %SET Sets a property in the VideoCapture. % % cap.set(PropertyName, value) % % The method set a Property value of VideoCapture. % PropertyName can be one of the followings: % % 'PosMsec' Current position of the video file in milliseconds or video capture timestamp. % 'PosFrames' 0-based index of the frame to be decoded/captured next. % 'AVIRatio' Relative position of the video file: 0 - start of the film, 1 - end of the film. % 'FrameWidth' Width of the frames in the video stream. % 'FrameHeight' Height of the frames in the video stream. % 'FPS' Frame rate. % 'FourCC' 4-character code of codec. % 'FrameCount' Number of frames in the video file. % 'Format' Format of the Mat objects returned by retrieve() . % 'Mode' Backend-specific value indicating the current capture mode. % 'Brightness' Brightness of the image (only for cameras). % 'Contrast' Contrast of the image (only for cameras). % 'Saturation' Saturation of the image (only for cameras). % 'Hue' Hue of the image (only for cameras). % 'Gain' Gain of the image (only for cameras). % 'Exposure' Exposure (only for cameras). % 'ConvertRGB' Boolean flags indicating whether images should be converted to RGB. % 'Rectification' Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently) % % See also cv.VideoCapture % VideoCapture_(this.id, 'set', key, value); end end methods (Hidden = true) function successFlag = open(this, filename) %OPEN Open video file or a capturing device for video capturing % % ## Output % * __retval__ bool, true if successful % % The methods release() to close the already opened file or camera. % Parameters are the same as in the constructor. % % See also cv.VideoCapture.isOpened % if nargin < 1, filename = 0; end successFlag = VideoCapture_(this.id, 'open', filename); end function flag = isOpened(this) %ISOPENED Returns true if video capturing has been initialized already. % % ## Output % * __retval__ bool, return value % % If the previous call to constructor or open() succeeded, the method returns true. % % See also cv.VideoCapture.open % flag = VideoCapture_(this.id, 'isOpened'); end function release(this) %RELEASE Closes video file or capturing device. % % The methods are automatically called by subsequent open() and by destructor. % % See also cv.VideoCapture.open % VideoCapture_(this.id, 'release'); end function successFlag = grab(this) %GRAB Grabs the next frame from video file or capturing device. % % ## Output % * __successFlag__ bool, success flag % % The 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 % grab() for each camera and after that call the slower method 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. % % See also cv.VideoCapture.read cv.VideoCapture.retrieve % successFlag = VideoCapture_(this.id, 'grab'); end function frame = retrieve(this) %RETRIEVE Decodes and returns the grabbed video frame. % % The function 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 function returns an empty matrix. % % See also cv.VideoCapture.read cv.VideoCapture.grab % frame = VideoCapture_(this.id, 'retrieve'); end end end