Grabs the next frame from video file or capturing device

successFlag = cap.grab()

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 cv.VideoCapture/grab for each camera and after that call the slower method cv.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 cv.VideoCapture/grab first and then call cv.VideoCapture.retrieve one or more times with different values of the channel parameter StreamIdx.