For some pieces on this website, a video is included showing the keys on the keyboards as they are being played. The videos only show the keys actually in use in the piece.
The lower keyboard is the pedal keyboard, for which the keys are displayed as buttons. That is only to save on screen size. The actual pedal keys will have the width and spacing of ordinary organ pedal keys and about the length of a shoe.
The horizontal line in the upper left hand corner indicates a manual octave span, which is 90% of the same on an ordinary organ.
Occasionally you may see a key with a yellow edge popping up. That signals a melodic syntonic comma coming up; a red edge marks where it lands. Syntonic commas are only signalled when there is less than half a second between the two tones. That is an arbitrary time interval obviously; syntonic commas may irritate with longer time intervals between the two tones. Please be aware that the tones that make up a syntonic comma may be in different octaves, or even on different keyboards.
The video does not show stops being switched on and off, nor have pitch shift actions been rendered (yet).