Flopping webcam input horizontally

or

ofPushMatrix();
ofTranslate(video.getWidth(),0);
ofScale(-1,1)
video.draw(0,0);
ofPopMatrix();

The grabber.getPixelsRef().mirror() approach will (AFAIK) be slower than the above or @arturo's method because it actually modifies the underlying pixels vs. using the graphics card to draw it to the screen flipped.