question: grabs the next frame from video file or capturing device . the methods/functions grab the next frame from video file or camera and return 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 . see https://github.com/itseez/opencv/tree/master/samples/cpp/openni_capture.cpp concode_field_sep long nativeObj concode_field_sep boolean n_isOpened concode_elem_sep boolean n_read concode_elem_sep boolean isOpened concode_elem_sep boolean read concode_elem_sep boolean set concode_elem_sep void release concode_elem_sep boolean n_set concode_elem_sep void n_delete concode_elem_sep void n_release concode_elem_sep List<Size> getSupportedPreviewSizes concode_elem_sep String n_getSupportedPreviewSizes concode_elem_sep boolean n_retrieve concode_elem_sep boolean n_retrieve concode_elem_sep double get concode_elem_sep boolean n_open concode_elem_sep boolean n_open concode_elem_sep boolean retrieve concode_elem_sep boolean retrieve concode_elem_sep void finalize concode_elem_sep long n_VideoCapture concode_elem_sep long n_VideoCapture concode_elem_sep long n_VideoCapture concode_elem_sep boolean n_grab concode_elem_sep boolean open concode_elem_sep double n_get
target: boolean function ( ) { boolean loc0 = n_grab ( nativeObj ) ; return loc0 ; }