[MEncoder-users] new doom9 codec comparission (submission)

Rich Felker dalias at aerifal.cx
Wed Dec 14 05:35:22 CET 2005

On Tue, Dec 13, 2005 at 03:10:50PM -0800, Corey Hickey wrote:
> Doom9 Feedback Hotline wrote:
> >>Aww, crud. Please do mention that a viable method exists for 3-pass. I'm
> >>going to write it up and submit a patch for DOCS/tech/snow.txt.
> > 
> > Well, why the need for 3 passes? Wouldn't a not so smart first pass with 
> > subsequent passes number 2 and 3 end up okay either way regardless of pass 
> > 1?
> I am 90% sure of the following.
> The second pass can meet the target bitrate as long as lmin is
> sufficiently low (vqmin is ignored). The second pass of the settings I
> gave you came up short because the default lmin=2 was too high. Snow is
> more efficient than mpeg-4 and needs to have lower quantizers to use as
> much data.

It has nothing to do with efficiency. Snow and mpeg4 quantizer levels
just aren't at all comparable. q=2 means totally different things in
snow and mpeg4.

> 2. Lowering lmin too far results in snow using quantizers for some
> scenes that are lower than necessary and forces other scenes to use
> higher quantizers. This looks a little bit better in low-motion parts of
> the movie and much worse in high-motion parts.

Same applies to mpeg4. You need to set lmin to whatever the highest
value that still looks "perfect" is. Probably something between 1.2
and 1.8...


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