[FFmpeg-devel] [RFC] faster vp3 unpack_vlc

[Reimar Döffinger]

On Tue, Jun 03, 2008 at 10:00:06PM -0700, Mike Melanson wrote:
> Reimar D?ffinger wrote:
> > Hello,
> > because of some user reports I downloaded the Ogg version of this:
> > http://www.bigbuckbunny.org/index.php/download/ and was surprised how
> > very slow it was.
> > Oprofile told me, that > 40 of decoding time was spent in unpack_vlcs.
> > It looks like a cache issue, since splitting one array out of the struct
> > as in attached patch brings it down to 28% of total time.
> > I have the feeling that this is a case where the data structure just
> > plain does not match the problem, but at least it is a start.
> > What are your opinions? Seems Mike is the maintainer of this file,
> > what do you think?
> 
> I'm still thinking about it. Don't remember enough about the algorithm 
> (allegedly, I'm mentoring an encoder this summer, too).
> 
> Do the changes work?

As far as I can tell. They should basically be only cosmetic.

> Are they measurably faster?

Well, I am no good at proper benchmarks, but with above file,
mplayer -nosound -benchmark -vo xv big_buck_bunny_1080p_stereo.ogg -demuxer lavf -frames 400
takes 26 seconds to decode with original code and 22 after the change.

Greetings,
Reimar D?ffinger