My guess is your K's are either when you're taking or swinging & missing on pitches lower in the strike zone?
I think it's because your swing is a bit stiff and controlled and the bat doesn't "whip" through the zone as much as you seem to 'pull" it or "guide" it through the zone?
Your follow-through really tells me that.
This happens to a lot of kids as they try to "find the ball" with the bat, instead of seeing it
and trusting the hands!
As has been said, let the lower half provide the propulsion, and let the hands drive through.
Loosen up the shoulders & hands and I think you'll make better contact.
Secondly, your back side load is really going to make you susceptible to the off-speed stuff. Get a better rhythm and stay back a bit longer.
Now follow me on this:
My guess is that your bat speed is fairly slow because you are restricting the swing with your arms & hands providing too much of the force.
So, to compensate, you load quicker and get out on your front side too soon.
(see pop-up on first video)
Sometimes, you can get away with that on a pitch up and out over the plate. (like the one the guy threw you on a 1-2 count)
But in on you is going to be a pop-up, and low and away is going to be a K or a ground ball to SS or 2nd.
If you use the lower half better, you will overcome that and the swing will be looser and easier but quicker through the zone.
Good Luck, and remember:
"Trust the Hands"