[MEncoder-users] new doom9 codec comparission

[Matthias Wieser]

Am Donnerstag, 8. Dezember 2005 08:55 schrieb Corey Hickey:
> Rich Felker wrote:
> >>>>Unfortunately, the quality drop from using threads=2 is, in my
> >>>> opinion, unacceptable.
> >>>
> >>>Definitely. I'm against using threads.
> >>
> >>Last night, on a whim, I decided to test qpel. Tests published by
> >> Rémi Guyomarch a few years ago showed a definite PSNR improvement
> >> from using qpel. My own tests confirmed that. Later on, I found that
> >> qpel was decreasing PSNR, and tests by a few other people confirmed
> >> that.
> >>
> >>Now, oddly enough, adding qpel raised the PSNR from 42.66 to 42.96,
> >> with a definite corresponding quality improvement. I can't say
> >> whether qpel should be recommended in general, but it obviously
> >> helps under these specific circumstances.
> >>
> >>Meanwhile, Michael had fixed the PSNR calculation for multithreaded
> >>encoding (thanks, Michael), so I ran a test with threads=2 and qpel.
> >>This brought PSNR down to 42.92, and I can see only a very very
> >> slight decrease in overall quality. Although "qpel" is the best,
> >>"qpel:threads=2" still looks a little better than omitting both
> >> options.
> >
> > If there's ANY visible decrease in quality, do not use threads.
> > Simple as that. It's stupid for an encoding benchmark anyway since no
> > one has or uses multi-cpu machines for encoding, since they're a
> > waste of money, electricity, etc. etc. etc. I don't want to see lavc
> > getting chewed out for bad image quality because someone wanted to
> > save a little time by using a dual-cpu system to encode at lower
> > quality...
>
> Ok. If you feel that strongly about it then I'll leave threads=2 out.
> I'm pretty much neutral at this point (not to mention getting a little
> tired of running a zillion tests).

If you think it makes lavc look better in the doom9 comparison, leave 
threads=2 out. But please don't leave threads=2 out only because one 
person does not like dual-core CPUs.


> Anyway, what I was getting at was that it should be possible to have
> significantly better performance at very little loss of quality by
> combining threads=2 with qpel.

Sounds good!

> I wish I had access to a dual-core/dual-processor machine so I could
> actually provide some better performance numbers. The reason my
> argument is so shaky is that I can't get the actual data, just what
> "ought to" happen.

Some actual benchmarks:
http://www.linuxhardware.org/article.pl?sid=05/07/11/185212&mode=thread/
Athlon 64, 2.4GHz
  Single core: 22minutes
  Dual core: 17minutes

Regards,
  Matthias