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

[Fabio S.]

> >>> 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.
>
> No, you cannot use two-pass mode directly when capturing from TV,
> because both passes have to be done on the same source; unless the exact
> same signal is going to be sent twice and you can catch it identically
> both times, you aren't going to get that with TV capture. However, if
> you capture to a different (preferably lossless) format from TV, you can
> then use two-pass mode on that.
>
> 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.
>
> If that isn't what you wanted to know, please try to clarify the
> question.

Yes it is.
I made some guess: you confirmed them and explained what I left out. Thanks.
I imagine that going more into the details of two-pass encoding would be
rather technical and not more clarifying for an uninitiated person like me.

Fabio