[MEncoder-users] two pass encoding with pullup

[Guillaume Poirier]

Hi,

On Apr 5, 2005 3:10 PM, Winterbird <winterbird at anime-avatar.net> wrote:
> Hans-Carl Oberdalhoff wrote:
> >Am Dienstag, 5. April 2005 08:58 schrieb Winterbird:
> >You should also leave the bitrate (rather: all lavc-options) the same on both
> >passes!
> >Only exception: If you want the first pass to be fast, you can use the
> >"turbo"-option on it. This will deactivate cpu-intensive options, without
> >screwing 2pass up.
> >
> >
> OK... Acctually I thought that the bitrate didn't really matter in the
> first pass...

It does, but not _that_ much. Please have a look at Loren's
explanation of how to tweak 2-pass rate control at
http://www.mplayerhq.hu/DOCS/tech/encoding-tips.txt
Basically, you might what to encode first pass at constant quant if
the final movie ends up being encoded with a similar average quant,
and if you tweak a bit the option vqcomp.
As far as I'm concerned, I encode first pass with a constant quant of
2, and set vqcomp to 0.7.
Then in the second (an up) passes, I use the "normal" bitrate.
That might be suboptimal, but I've been quite happy with the results I've had.


> qns is *very* cpu intensive, that's why I didn't use it in the first
> pass, it takes quite some time to encode something on my box... I might
> try the turbo option...

The turbo option is supposed to deactivate all CPU-hungry options that
aren't worth it in the first pass, and ONLY in the first pass, so my
advice would be to add it all the time to you encoding option set, as
if it's not the first pass, it just does nothing at all.
The problem is that it leads to a small decrease of PSNR, but not
something you might actually see (unless you're an alien ;-) ).

Guillaume