[Theora-dev] Re: MMX/mmxext optimisations
Adam D. Moss
adam at gimp.org
Tue Aug 24 03:54:36 PDT 2004
Wim Taymans wrote:
> Attached is a patch against libtheora-1.0alpha3 that adds mmx and mmxext
> optimisations to theora. It uses gcc inline assembler and has cpu
> detection code. Most functions are optimised except for the IDCT and
> some post processing functions. The focus was mainly on the encoder part
> as we want to stream the KDE conference (which takes place this weekend)
> in a little higher resolution than 64x40 :)
> Encoding performance of a 320x240 video at least got a 2x increase.
> Further optimisations require better algorithms.
This is great!
Encoding performance seems to have at least doubled, and on my
Athlon ('classic') I've even seen 4x encoding speed.
One down size is that to my eye, mmx-encoded theora videos are
slightly blurrier than their standard counterparts, for a fixed
target bitrate. Also, for a fixed quality factor, the files seem
quite a lot smaller (but not particularly worse-looking on brief
inspection, which is odd and counter-intuitive given the first
observation, but I'm not complaining).
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