[vorbis] Mono wavs with b4

[Moritz Grimm]

Craig Dickson wrote:
> When I encode a monophonic wav file, I would expect the resulting ogg file
> to be at about half the bit rate specified on the command line, as stated in
> the "oggenc -h" help text: "The 6 modes are approximately 112, 128, 160,
> 192, 256, and 350 kbps (for stereo 44.1kHz input. Halve these numbers for
> mono input).".

The last sentence means that you should halve those numbers yourself,
because these values are the 6 modes for stereo input.

I tried it on a mono file with 'oggenc -b 80 input.wav' and it worked
fine - i got a mono .ogg with an ABR of 83kbit/s out of that.

This really is confusing, and I have no idea without consulting my
pocket calculator what bitrates I should choose when actually having an
multichannel input file. I think it might be a good idea to give oggenc,
in addition to the -b option, an option '-m' (for 'mode', just as an
example and it's still unused, btw) followed by a number between 1 and 6
and then let oggenc choose the appropriate bitrate for the input file.
(Would make it very useful when batch-encoding .wavs with varying
amounts of channels at the same quality level (that is what most users
want, I guess).) A nice side-effect would be the transparent encoding of
non-44.1kHz waves ... getting ~70kbit/s when using -b 112 is somewhat
irritating.

What I would not want is to replace the -b option. Being able to set the
bitrate directly surely is useful from time to time.

Assuming, the option '-m 2' (which should be default then, because -b
128 is default) gives a stereo_input.wav around 128kbit/s, it should
give a mono_input.wav 64kbit/s, a 3channel_input.wav 192kbit/s, etc.

Then, there's something else I don't understand. Quoting
http://www.xiph.org/ogg/vorbis/: "[...] for high quality (44.1-48.0kHz,
16+ bit, polyphonic) audio and music at fixed and variable bitrates from
16 to 128 kbps/channel."

How come? oggenc doesn't support 32kbit/s for stereo files right now
(?), but I guess this still hast to be implemented anyways ... but on
the other hand oggenc seems to support 350kbit/s for stereo files, which
is 175kbit/s per channel and not 128kbit/s. Or is 350kbit/s intended
only for 3channel-input with 117kbit/s per channel?

It'd be great if someone could make things more clear for the 1.0
release ...

Bye,

Moritz

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