[MPlayer-users] Two-passes encoding - What happens exactly?

[Alain Barthélemy]

Le mardi 01 juin 2004, 16:08:49 ou environ The Wanderer <inverseparadox at comcast.net> a écrit:
> Alain Barthélemy wrote:
> 
> >Le Tuesday 01 June 2004, 04:32:23 ou environ The Wanderer
> ><inverseparadox at comcast.net> a écrit:
> >
> >>Fabio S. wrote:
> >>
> >>>It is the same for me: it would be nice if somebody would explain
> >>>exactly (in a qualitative way) what happens during two pass
> >>>encoding, how to use it for (as you said: do we need to rewrite
> >>>all options?) and when we can use it (is it possible to use it
> >>>for capturing from the tv?)
> >>
> >>Well, I'm not sure I quite understand what you're asking in the
> >>first of those three cases, but I can take a shot at the others.
> >>
> >>Yes, you need to use all of the same options on both passes; there
> >>are apparently a few which you can vary slightly without hurting
> >>anything, but for the most part changing the options between passes
> >>will mess things up.
> >
> >My question was not to know if we could change options between two
> >passes but if we had to keep the same options between the first
> >original TV-signal encoding and the two passes. You answered it at
> >your first reply. The -lavcopts options had to be retyped.
> 
> ...I don't know if I quite follow this. Do you mean that you're encoding
> with libavcodec from TV, and then using two-pass mode on the result?
> 
> That's not as good as encoding to something lossless from TV and then
> using two-pass mode on the result, but it will work. However, it is
> *not* necessary to keep the same options between the initial from-TV
> encoding and the two-pass encoding; it is only necessary to keep all of
> the same options between the two passes.
> 
> -- 
>       The Wanderer
> 

Thanks but explain "lossless" (without loss?). When I started with
MPlayer/Mencoder I understood that I had first to encode the TV-signal with
libavcodec. In fact I was "adviced" to first encode with a high vbitrate and
then to reduce the vbitrate (to obtain a 700Mb file) with a two-passes
encoding. No "lossless" at that time. I did a subsequent two-passes encoding
only when I had to crop the image or to reduce the vbitrate.

-- 
Alain Barthélemy
cassandre at bartydeux.be
http://bartydeux.be
Linux User #315631