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

[Alain Barthélemy]

Le Tuesday 01 June 2004, 04:32:23 ou environ The Wanderer <inverseparadox at comcast.net> a écrit:
> Fabio S. wrote:
> 
> >>>My question is. Do I have to recopy all the options? Sorry if it
> >>>is stupid.
> >
> >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.


> 
> As for the first question... as best I understand it, what happens is
> that during the first pass, MEncoder keeps track of which parts of the
> video need more bits than they're getting and which don't need as many,
> and writes that information to a file. In the second pass, it uses the
> information from that file to determine how many bits to allocate for
> each part, to achieve the best overall quality within the target bitrate.


Thanks for this answer. It was exactly what I asked. Let's call it a "cleaning"
of the code.



> 
> If that isn't what you wanted to know, please try to clarify the
> question.
> 
> -- 
>       The Wanderer never thought *he*'d be answering questions here...
> 
> Warning: Simply because I argue an issue does not mean I agree with any
> side of it.
> 
> A government exists to serve its citizens, not to control them.
> 
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-- 
Alain Barthélemy
cassandre at bartydeux.be
http://bartydeux.be
Linux User #315631