the insim app records a very small replay-data file for every racer (but only stores it when you complete the lap and if it's a new pb), made from the data MCI packets give. Then that replay-data is fed into your browser, javascript parses that and draws the 'cars' onto the map, which in turn is a background picture, generated on the fly by php, drawing the layout and racing lines (using that same replay-data file).