[vorbis] docs question

[gtgbr at gmx.net]

Haas Wernfried wrote:
> oggenc --help says:
>  -b, --bitrate        Choose a nominal bitrate to encode at. Attempt
> while man oggenc says:
>        -b n, --bitrate=n
>               Sets  encoding  to  the  bitrate  closest  to n (in
>               kb/s).
> and
>        --managed
>               Set bitrate management mode. [..]

Yes, since --help doesn't mention --managed, the help-text is obviously
wrong. It works like this:

In most cases, you want full, quality-based VBR mode. You choose your
quality with the -q switch, from -1 to 10. 
Every quality settings comes with a so-called "nominal bitrate", for
example 112 kbps is the nominal bitrate for -q 3. The problem with those
nominal bitrates is that they're no more than mere hints on where the
actual average bitrate of the encoded song _might_ end up. You can also
select the quality level based on the nominal bitrate, just don't be
surprised if some quite different bitrate comes out in the end - this is
still full VBR. E.g. if you choose -b 112, this would equal -q 3 on
44.1kHz/stereo input.

If you want to use average bitrate encoding, with the bitrate management
engine, you have to explicitly enable it with the --managed switch.
--managed requires the -b switch, as we care about bitrates now. oggenc
-b 112 --managed file.wav would encode file.wav with bitrate management
and the goal of having a ~112kbps file in the end. Using bitrate
management comes at the cost of lower quality and much longer encoding
times, what you gain is more predictable file sizes.

<p>Moritz
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