[mg262]

Thanks, guys... but the beauty of AVISynth (as a package) is that it does all the slow to write, reference-requiring, technology-dependent parts like opening files and rendering, so that's where most of the credit should go!

I briefly tested sub pixel (1/4 pixel) accuracy in a rough form in C, and it helps a little, but the blocking and accuracy still much worse than that of MVTools. The last time I tried MVTools was at least 18 months ago (it's pretty rare that I work with non-animated material), and I hit substantial blocking... but now, at least on the source at hand, blocking seems very rare and its fast -- this runs at 50FPS:*

mvanalyse(source)
mvcompensate(source, last)

I was pretty disappointed with the comparative performance of this method -- the papers on it certainly give the impression that as well as being super-fast and producing true motion, it gave very good results with minimal blocking. It's possible that I made some silly mistake (and I'll check through), but the vector fields look pretty sensible. My particular interest was in trying to develop this for denoising scripts, and that seems relatively pointless now. Don't take that the wrong way -- I'm quite happy to try other things with it, it's just that denoising was the target I was heading towards. So, I'm not really sure where if anywhere to go from here... thoughts?

*Motion compensated scripts (e.g. MVBob) have the reputation of being really slow... why is this?

____________________
I ran across one simple deblocking method for truemotion motion compensation which I might as well repeat here:

Obtain motion vectors, then subdivide each block into four.
For each top-left subblock:

Replace the motion vector with the median of
-- original motion vector
-- vector from block to the left
-- vector from block above

Median is computed in x and y separately. (+Optionally, you discard the vector if it doesn't much one of the three above.) Other 3/4 sub blocks work in the obvious way.

AFAICS, the effect is to take a stair step and reduce to a stair step of half the size. The method is particularly intended not to introduce new motion vectors which didn't exist before.