I downloaded your file and have to agree that it is definitely “not smooth”. There appears to be some type of “shimmering” effect which is a bit disconcerting. The first part should be very smooth movement, but if you bring it into Vegas and look at it frame by frame, you will see that the movement presents a very odd pattern. E.g. movement left, then up, then down, then left. Sadly, I’m not the one to diagnose exactly what’s going on from just seeing the clip, but in any case, you will need to provide more info in terms of your source footage, frame rate, etc. and also your render settings.
wwaag