Jack.
That belt is far too loose and is clearly jumping sprocket teeth. Since the belt also drives the camshaft there is a real risk of damaging the valves or the piston crowns, which would entail a horrendously expensive repair bill. Do not attempt to run the engine, or even turn it over on the starter, until it has been put right. If that means towing it to a garage or workshop, so be it, but the engine must not be run.