[theora] No quality advantage with two-pass?

[Remco]

On Sat, Aug 29, 2009 at 4:22 AM, Remco<remco47 at gmail.com> wrote:
> The ffmpeg2theora chapter[1] of the Theora Cookbook says that the only
> advantage of two-pass encoding is that you can hit a specific target
> size. But isn't it so that you can reserve bits for difficult parts of
> a video, which improves the perceived quality? It may be true that
> Theora does quite alright without two passes, but it seems like a
> no-brainer to me that two passes will always be better.
>
> --
> Remco
>
> [1] http://en.flossmanuals.net/TheoraCookbook/FFMPEG2Theora
>

Oh, I think I get it now:

* Single-pass encoding with a constant quality will use more bits for
harder parts, and deliver the best possible file size for that
particular quality level, and vice-versa.

* Single-pass encoding with a constant file size will reduce quality
for harder parts.

* Two-pass encoding with a constant quality size is senseless, since a
single pass already delivers the best possible file size for the
quality.

* Two-pass encoding with a constant file size will use the first pass
to somehow learn which quality setting will produce the target file
size. Still, the result is a file with the best possible quality for
that file size, just like with single-pass constant quality encoding.
It's impossible to get more from the encoder.

-- 
Remco