hey , early on in the tape you are asking the dog more than once , and the dog is learning to pause . Then he goes down but you reward too fast , and are actually rewarding the dog as he is changing positions into a sit .
If he doesn't go down , move away , game finished. He follows you, so, he is asking for your attention , he is pushing your button to keep on playing . Then do ask him down. Stroke him. Calmly. stand up . He moves , go back to square one. He stays down then calmly put it on the floor in front of him. That way there is no chance of you drawing him (luring) out of position.
You could put it under your foot then move your foot.
Okay went back for a second or third look. I don't have a sound card on my computer at the moment ? so all I see is images . Look at the video yourself with no sound . You're doing a lot of movement with your hands. I wasn't clear what you were asking of the dog. Your hand signals should be very clean and clear .
Also am I right , you are asking the dog to sit (frame 6) and then going into a down. Teach one thing at a time.
Break it up . get dogs attention teach one thing , let's say you select "down" tell dog "down" reward -- release OK praise verbally and by stroke - get the dog connected to YOU not just the food. Move , ask dog down. Wherever you are the dog does this one thing "down" RELEASE - and he can't move till you release him. Ends confusion , no grey area.