On your drive side crank arm (the loose one) there should be a bolt or nut that attaches to the spindle, its probably coveredby a dust cap which you need to either unscrew or pop out (depending on style) you should be able to tighten the nut or bolt with a 14mm socket wrench or an 8mm hex wrench, riding with this kind of slop in the interface can cause irreperable damage to the arm, tighten it down reaal tight and cross your fingers
sorry I can't help you with the stem, I've never worked with adjustables before


*EDIT*
Just rewatched your video, seems the slop is on both sides indicating a loose BB, take it to a shop, you will require special tools