I'll start off from the beginning. Work on your patter. Honestly, I don't care what kind of cards you're using, nor that they're all different... I just want to see the trick. Sorry to say it, but that needs to be taken off.
Your Double from the center was horrible (no offense). It just looked awkward. Try to rotate the card using the edge of your fingers before turning the hand over, instead of grabbing it and rotation it. You'll find it makes the Double loads easier.
Now, once you managed to get the Double on top of the deck, you need to handle it more "fluidly". The turning over of the Double was... bad, to say the least. Try to make it more natural, as if you are truly handling one card.
Now, the second Double you also need to work on. Try to turn it over like the Bucks do when they're performing it; grab the right edges of the cards with your index finger and thumb of your right hand, and rotate it around your left thumb, turning it face up onto the deck.
At this point, you got to the change. It looked terribly awkward and suspicious. You flashed a bit right after the initial change, but then you went on to make it look even more suspicious by laying your hand on top of the deck and only allowing us to see the outer left pip of the card. Work on having your hand more natural and "fluid", like it's floating above the deck.
You also seemed to stumble while pulling the eight out of the center... it took way too long, as if the "instantaneous switch" was still taking place. Work on executing that "move" faster and more naturally, as if you were simply pulling it out of the middle.
I know you probably hate me by now because of all the critisicm I'm giving you, but I have a couple other things I would like to mention. First, your performance overall as a whole. It was dry and boring... two things you do NOT want to be as a magician, or a person in general. Try to be more entertaining... make me want to finish watching your video, instead of making my mouse draw ever closer to the big X in the corner. Like I always say: the performance gets 90% of your reactions... the other 10% goes to the effect itself.
And last, but not least, try not to sway back and forth so much while performing. It not only made it extremely hard to watch, but I also think I may have gotten a little seasick towards the end!
I'm sorry I was so harsh on you, but you really need to practice a bit more. Better luck next time!
