One problem with your video that makes it hard to T/S is that you are holding the camera with one hand while demonstrating the play with the other, making it hard to see any play occurring at the pivot points. If you could immobilize the camera and point it at the bottom of the pedal we might be able to help you better. Just from the clunking sound that I'm hearing I believe you have worn components, i.e. rod end bearings or bushings or both.
