Capture Video of an Application

Hi, I've a node-webkit application that displays an animation. I need a script to CAPTURE the animation, could be frame by frame, 15fps, 25fps or 30fps ... you can include ffmpeg to join all the captured frames (saved on a folder). IMPORTANT: Mind that this script should ONLY capture video from this node-webkit application regarding if there are other windows open or not, ONLY from this application ok? Should work on Windows and Mac. >>> RESEARCH what node webkit is before bidding as we need to use a FUNCTION to call your script to record the animation!