[MEncoder-users] new doom9 codec comparission

Rich Felker dalias at aerifal.cx
Sun Dec 4 05:06:31 CET 2005

On Sat, Dec 03, 2005 at 07:30:16PM -0800, Corey Hickey wrote:
> > And why such small vratetol?
> It's favorable for a codec to meet the requested bitrate precisely, and I've
> been using vratetol=1000 on my own testing for a while without noticing
> anything wrong. If you have, then please tell me and I'll relax it. For that
> matter, tell me if you even have misgivings. The default of 8000 would be
> ok, but if there are no ill effects to using 1000 then I figure we might as
> well.

IMO don't mess with ratetol unless the file size is very bad without
changing it.

> >> * I need to test vqcomp=0.7 or vqcomp=0.6
> >
> > Rich said something about keeping it at the default level of 0.5 on IRC
> > the other day.
> I've never tested this parameter, but at this point I think vqcomp=0.7
> assists encoding this material. Go to this page:
> http://www.doom9.org/index.html?/codecs-203-2.htm
> ...and take a look at how many of the screenshot frames are in the midst of
> lots of motion. In particular, look at the last shot with all the blue-green
> lightning, and look at how well the different codecs have preserved the
> texture of the concrete while the lightning jumps to a different place every
> frame. My own encodes aren't much of an improvement over the "ffvfw"
> screenshot.

I recommend low value of qcomp because: when encoding I often notice
that in the first pass, all the low motion scenes look beautiful,
while the high motion ones look anywhere from slightly bad to very
bad. During the second pass, if qcomp is very high, all the bits from
the low motion scenes get wasted on trying to make the high motion
scenes look good, and:
- low motion scenes look like blocky shit
- high motion scenes barely look better in all but a few extreme cases

So personally I prefer qcomp=0.5 or even 0.4. Of course if you're
using very high bitrates and insist that still frames look good even
during high motion, you may want qcomp=0.6 or 0.7.

All of my recommendations here are for moderate-bitrate encodes, e.g.
1-cd encodes of movies. For high-bitrate the game is different I

> > Oh, one more thing: what about B-frames?
> vmax_b_frames=2 helps PSNR significantly, but mencoder still doesn't
> properly maintain a-v sync when b frames are present. I'd like to use them,
> but it doesn't seem right to recommend an option that, although it helps the
> video itself, doesn't work properly with mencoder.

Sure, it's fine. No one will use mencoder for serious a/v sync anyway.
Instead they'll disable a/v sync entirely, encode audio & video
separately, and then remux. :)


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