How to set framerate for recording from webcam

you are right, looking at the code the QTKit will always throw the warning. You can probably do a work around for the framerate issue by sampling the frames at the rate you want it to be. like in update check if enough time has passed since you last sampled a frame with something like

if(ofGetElapsedTimef() - timeSinceLastFrame > 1.0/framerate){
  frame = vidGrabber.getPixels();
  timeSinceLastFrame = ofGetElapsedTimef();
}

thats not perfect but it should work