Be careful with the concept about pulling your feet back underneath you as Ken suggested. There is an important time for this, which is as you crest the bump. HOWEVER, its also important as you go down the back side of the bump to reach down with your toes and push those legs down and forward as much as possible, to the point that as you reach the flat spot it may seem like your feet are now in front of your CM rather than underneath it. As you come down into the flat space you will begin to compress, which will move your COM forward and that is when you then start to pull your feet back again.
Note that if you hold your feet too far back as you go down the backside, when you hit the next flat space if your feet are still underneath your butt, you may very likely feel catapulted over the handlebars.
Mark Ellling's books has some great coverage of this concept. Check it out.
If you watch WC mogul guys, their feet are indeed moving back under the butt and back out forward again. But the interesting thing is that their hip is nearly always pretty far back in relation to their knees, feet and slope angle.
When you're skiing down a steep non-mogul slope, you want to maintain a centered stance relative to the slope, which usually means your body is tipped foward, somewhat 90 degress to the angle of the slope. However, in bumps its a different situation because each bump is adding and taking away gigantic amounts of force as your crest each one. If you were leaning out 90 degrees to the slope angle you'd quite possibly be vaulted over the handle bars when you hit a bump, and if you pull your feet under your butt too fast and too soon, then your COM will be too far forward and give you similar results, not to mention a limited range of absorption motion in your lower body.
I agree with others about heading down the fallline, however if you were in a ski instructor course, they generally don't want to see that, they want to see you complete turns. Also, you have some fatty skis on, which aren't helping you. They make every single edge change more laborious and slow. That makes zipperline bump skiing less of an option.
Some general tips
- Make sure you're looking 2 bumps ahead, not the bump in front of you. 3 bumps ahead even better. Always scanning up there. When you do that its like being Neo in the Matrix and all of a sudden everything slows down and the bumps somehow seem to be wider apart and easier to turn around. This point should not be underestimated. Trust me. It takes a bit to get used to this, but huge payoffs.
- Don't miss any pole plants, even if you just set the pole basket down on the backside of the bump. Try to get the pole plant as far down the backside of the bump as you can. NOT on the flat space on top.
- I saw you trying to extend down the back of each bump. GOOD JOB. That was probably freezing up some of your active flexion to absorb. So just keep working on that. Extend as actively as possible...keep focusing on that. But also flex as much as possible as you crest each bump. Don't just think about absorb absorb absorb, nor about extend, extend, extend. Think Absorb-extend-absorb-extend and do them both very actively. A huge part of success in the bumps is getting a rythmn going and you are actively extending and absorbing in a coordinated way with each turn. Personally, I don't think you will have to worry so much about whether you're pulling your feet back under your butt or not. (not now). Just stay what feels like center balanced and focus on the other tasks. Later on if you have problems falling into the back seat that could be addressed.
Every time you extend, drive your pelvis forward and the tips of your toes down the back of the bump. Every time you absorb pull your knees to your chest as you reach for your pole plant and also think about dorsiflexing your ankle about that time. Tip and engage your edges as you extend down the backside of the bump. There is a huge area of snow on the backside of that bump which you don't actually see from above it. Your goal is to carve the top part of every turn on that area of snow (not on the flat place on top of the bump). Actually this area of snow I'm talking about is to be more precise around the OUTSIDE and DOWNHILL side of the bump in relation to where you are as you approach it.
Don't just depart the top of one bump with your vision set on the next flat spot. Hopefully your vision is 2 bumps ahead anyway and this is one reason why. The instant you pass the crest of the bump you should be engaging your edges to scarve around the outside/backside of that bump so that you will ideally come upon the next flat spot rather softly instead of free falling down to it in a gigantic heap of flesh and gortex.
The trick is to do that without getting all frozen legged trying to think about all this stuff. The active extension/flexion is totally a huge key. If you did nothing else but focus on that a while I think it would do you well.