[MEncoder-users] new doom9 codec comparission

Rich Felker dalias at aerifal.cx
Thu Dec 8 08:07:08 CET 2005

On Wed, Dec 07, 2005 at 05:41:57PM -0800, Corey Hickey 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...

If we want to make lavc look fast, why not do everything else that
gets performance at the expense of quality too? Set mbd=0, disable all
options like qpel, 4mv, ... etc..... :(


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