[vorbis] Very low bitrate encoding

[msmith at labyrinth.net.au]

> Hello Michael, 
> 
> thanks for your answer, but I don´t want to resample or downmix the
> source file prior to the encoding process, i want a resulting ogg file
> with a constant bitrate of less than 45Kbit/s which is, apparently, the
> fixed minimum for the encoding tools like OggDrop and the command line
> version as well.
> 

No, that's completely untrue. The tools (actually, the encoding library) have
a minimum bitrate they can encode at for a given sample rate and number of
channels. However, they're entirely capable of encoding at lower bitrates -
that's what the --downmix and --resample options are _for_. Like pretty much
every other codec out there, vorbis can't encode 44.1 kHz/stereo at (for
example) 8 kbps. Some encoders will automatically (without prompting the user)
resample the input to reach these low bitrates. Some, like oggenc, will not do
this automatically, but rather require the user to specifically request
resampling.

> > the managed bitrate modes. If you merely want to encode at a 
> > lower bitrate (but one which may vary) you can still use the quality
> modes.
> 
> I am after constant bitrates of 32, 24, 16, and even 8 or less Kbit/s. I
> didn´t manage to get a stream which is less than 45KBit/s using the
> normal command line tool or Oggdrop.

Then use the options described.

Michael

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