[XviD-devel] Re: qpel smearing/noise problem

[suxen_drol]

> hi,

> we need to replace our idct. the present mmx/xmm code (peter
> gubanov/mpeg2dec) produces errors, which become quite visibile in
> quarterpel mode. our current integer idct also produces qpels errors..
> which makes me curious about the sse2/ppc/ia64 stuff.
> 
> anyway, i think we should switch to michael niedermayer/ffmpeg's
> simple_idct. it is fast and produces much less error.
> simple_idct_mmx is written in gas... so will anyone object to me
> commiting a nasm'd version?
> 

i retract my previous statement
it seems simple_idct is prone to h+v qpel interpolation error.
(where as the mpeg2dec idct was more prone to h qpel interpolation)

i conclude that quarterpel amplifies idct error.
maybe wee need to enforce an intra macroblock refresh every 132/4 frames,
or use ieee_floating_point_reference_idct, or maybe pull qpel
entirely? :-(

this explains why h.264/avc uses an integer transform for 8th & 16th-pel
interpolation.

-- pete; life is like a box of ammo