Your shooting arm's not aligned well. You're a very good player, and you seem to have excellent control, but your stroke will gain power and consistency if you straighten it out.
The trouble is your right shoulder is not directly above the cue. Instead, it's well outside the cue, meaning your lower arm is bent back in toward your body, instead of hanging straight up and down. Because of this, if you were to just move your lower arm straight back and forth, using your elbow as a simple hinge, with no other movement, your stroke would have a banana curve, because the plane of this arm swing would not be lined up with the shot. You have a very compact stroke (and there's nothing wrong with that) so this curve is not pronounced, but it still means you're probably getting more muscles involved than necessary to correct this arm swing, and that means you're holding your stroke back.
So do this: you have your chin over top of the cue. So turn your shoulders so they're at more of an angle with the shot; you'll rotate your right shoulder back and inward. You can use your neck a little also to move your head a bit to your right, to make it easier for your right shoulder to be behind your chin, in line with the shot. You'll probably also want to move your hips further to your left, so that this shoulder rotation doesn't involve an uncomfortable twisting of your torso.
So now that your shoulder is straight over the cue, you'll probably also need to tuck your right elbow back in closer to your body, so that it is also directly over the cue. If your chin, your shoulder, AND your elbow are all over top of the cue, then your forearm must be hanging straight down (perpendicular to the floor) from your elbow to the cue. You clearly have the capability to video yourself, which will help you see when you've gotten things properly in line.
Now, try to stroke straight. You're used to compensating for funny alignment, so you'll be off at first, but once you get that stroke straight again with your new correct alignment, your forearm will be swinging straight back and forth from your elbow, with almost no effort whatsoever. Moving the cue back involves the tricep muscle contracting, and NO OTHER TENSION. Moving the cue forward involves your bicep muscle contracting, and NO OTHER TENSION. This movement is hugely more efficient and controllable than the one you were doing before, involving many small muscles to make your forearm swing straight even though that's not where your elbow hinge pointed.
You should notice immediately that you get more stroke velocity (more action) with less effort, with the new stroke. Over time with the new stroke, you'll find that you can also be much more accurate on long hard shots, because it's less of a feat of coordination to move your arm swiftly and accurately in the forward stroke, now that you're using one simple muscle contraction instead of several smaller ones in concert.
-Andrew
EDIT: Oh yeah, like the other posters are saying, you're clearly an excellent 9-ball player, and I don't see any reason you couldn't become a truly great player. I just posted a constructive criticism of your stroke because that's what you asked for.
