This is my first foray into animating from video. What that means, if not obvious, is that I'm trying to match a figure's motions to that of a person in a video. The camera and person are 'fixed', so there is no need to make camera or body adjustments. The problem that I am encountering is that Poser's spline interpolation is doing a lot of over-adjusting and between keyframes (depending on the previous key and next key between two nearly similar keys, the spline curve can go in a large arc) and making motions more linear than accelerated. I was wondering if it would be a better idea to do all of the keyframing using linear interpolation and then converting to spline as needed. Tips and tricks appreciated! :)

Yes, start with everything linear and convert to spline afterward, when the entire "future" of each motion is already constrained so the spline can't go wild with its psychic predictions. If you're matching frequently enough (like twice per second) the linear will probably look rounded enough anyway.

Thanks, ockham! I was hoping this would be a good approach. Those 'psychic predictions' are just about as good as the real thing... ;0)