He looks like a lovely boy and you seem to be a rider with a lot of potential!
What I think is wrong here is not understanding what an 'outline' is. There are times where your horse drops his head...this good be because he is relaxed (good!) or because he is evading being pulled in the mouth (bad!). When we ask our horses for an outline it actually has very little to do with the head, and much to do with the back and HQ. It is hard to measure impulsion in slo-mo, but it does look as if he is quite happy to shuffle along without working too hard, like most horses do! A frame is created by a forward aid being ridden into a restraining aid...asking the power to come from behind and up through his back...by default the head will drop.
At your level I would work on getting a steady contact and working on nice bends and straight lines - if you look at around 0:51 you are coming around a corner flexed to the outside. That will throw off his balance and he won't be able to engage his back effectively. Once you are able to get him moving straight and rythmically he will be able to give you much more!
Would love to see your video after tonight :)