you're using a little knee bend on the first rep on your press and taking too long to get under the bar on the way up. the best way i've figured out how to fix this is to look down at the floor maybe 10 feet in front of you for the duration of the exercise. your head will bob right back down where it was as soon as it can get past the bar. it really feels like it's added weight to my press.
it's also a little unclear where you're breathing. i'm pretty sure you're "bouncing" the bar, which has you breathing at the top, but you kind of pump through the reps one after the other. normally when breathing at the top, lockout lasts a second while you breath deep and hold it before you start dropping the weight for the next rep. you also seem to slow the bar down quite a bit before it finally hits your chest. this limits the help you can get from the stretch reflex at the bottom.
here's a video of my friend pressing using the bounce method for a visual:
http://www.youtube.com/watch?v=ByYpqpnVgew - notice how he holds the bar overhead between reps and gets more of a bounce at the bottom. he should be getting his breath in while the bar is still overhead, but you can see how he gets it and holds it before the bar is halfway down. his right elbow is messed up and he can't get it straight up and down fwiw (he can't touch his right shoulder with his right hand).