[Vorbis] ultra-low bitrate stream?

[Michael Smith]

On Thu, 06 Jan 2005 16:07:14 +0800, Qiangning Hong <hongqn at gmail.com> wrote:
> I am writing a long-run sound recording application using OggVorbis.
> The user can adjust sound quality parameter to make balance between
> storage space and sound quality.
> 
> The input sound is 22050Hz, mono.  To maximize the recording capability
> on a given storage volume, we want the result bitrate as low as possible.
> 
> I use -q0 parameter and it produces a 32.0kbps stream.  It is too high
> (our competitor using Microsoft WMA can produce 16kbps streams at the
> lowest quality setting).  I tried -q-1 and the bitrate is still
> 24.2kbps.  -q-2 and -b16 both produce error messages.

You should try using a lower sampling rate (WMA is quite likely doing
this internally without telling you). Oggenc can resample on the fly
for you. e.g.
   "oggenc -q -1 --resample 11025 file.wav"

There's also a third-party set of patches to libvorbis which adds an
ultra-low-bitrate "-q -2" mode - I can't remember the name, but a few
searches should turn it up for you, if you want to try that. That's
probably not neccesarily if resampling is sufficient to reach your
goals, though.

You could also try using a managed bitrate mode with a fixed maximum
bitrate, but this is unlikely to help much (and would probably
substantially degrade quality).

Mike